Industrial Minerals: 200 Years and Going Strong, D. Conrad and D. Vanacek , 1990 and updated in 2005 (S. King) and 2016.
The diverse geology of Vermont was highlighted in 1992 with the passage of Act Number 221 designating a State Rock. Intense lobbying by various mineral industries resulted in Vermont naming not one but three state rocks – granite, marble and slate. The legislation also designated grossular garnet the State Gem and talc the State Mineral.
While comprising only 9,609 square miles of land area, Vermont is notable for the variety of its mineral resources. The complexity of the bedrock geology is largely the result of the Taconic, Acadian, and to some degree the Alleghenian orogenies, or mountain forming events. Given the resultant bedrock structure and chemistry, Vermont provides a useful paradigm for plate tectonic theory.
The oldest rocks in the region are exposed within the core of the Green Mountain physiographic province in southern Vermont. The Precambrian "Grenville" age gneisses, quartzites, and marbles record metamorphism that occurred 1100 to 1300 million years ago. This series of rocks extends beneath the cover of younger rocks into the Grenville province of the Canadian Shield.
The area experienced a period of quiescence until about 650 million years ago, when crustal stretching (Wilson cycle) began to form the proto-Atlantic Iapetus Ocean. Iapetus continued to widen, separating Africa and North America, until about 450 million years ago. At that time, a shallow sea covered New England and formed the shelf sequence of carbonate and siliciclastic deposits located in the Champlain Valley and Vermont Valley physiographic provinces. This Cambro-Ordovician shelf sequence grades eastward into shales, turbidites and breccias that record a westward transgressive marine environment. The sequence was faulted and folded during the Taconic orogeny, the most prominent fault being the Champlain Thrust fault, which placed Lower Cambrian rocks over Middle Ordovician shales.
During the Middle Ordovician, Iapetus began to close due to compressional forces affecting the crust. A subduction zone formed offshore, wherein a western segment of oceanic crust was forced under an eastern portion. The resultant island arc system, known as the Bronson Hill anticlinorium, forms a major structural feature of the Appalachian system; associated domes appear at irregular intervals from New Hampshire to Long Island Sound.
Exposed in southwestern Vermont in the Taconic Highlands province is the Taconic allochthon, a complex mass of rock emplaced during the Late Middle to Late Ordovician. The mass is composed of deep-water argillaceous sediments with interbedded limestones, sandstones, and greywacke. The sequence contains several thrust slices that were emplaced westward on the shallow-water carbonate platform from either the Green Mountains or possibly farther west at the longitude of the Connecticut River.
Taken together, the orogenic events that affected this area could be considered pulses of a single, extended phenomenon. The Taconic orogeny, usually assigned to Late Ordovician time, marked the collision of the Bronson Hill island arc system with the continent. Block faulting, prevalent during the early compressional phase was followed by intensive thrust faulting. The continued crustal shortening folded and faulted rocks as far inland as the Allegheny Plateau and the Adirondack Mountains. It is estimated that the crust compressed 600 miles, resulting in significant changes in topography, drainage, and sedimentation. Slivers of basaltic ocean crust were transported to the continent and altered by heat via deep crustal faulting and shearing. These slivers represent the ophiolite occurrences within the state and are locations for talc, serpentine, and asbestos mining.
The Taconian event was followed by a period of relative tectonic calm between 435 and 375 million years ago. The Acadian mountain-building sequence, occurring between 375 and 335 million years ago during the Middle Devonian, marked the final closing of the proto-Atlantic basin and collision of the continents. The Acadian event caused the reactivation of Taconian faults, as well as significant folding and metamorphic overprinting. Precambrian rocks now exposed in the core of the Green Mountains and the Athens and Chester domes represent units raised by Acadian folding and faulting, and later exposed by erosion. Intrusion of the New Hampshire Plutonic Suite plutons, which include large igneous bodies in Vermont, occurred late in the Acadian event.
Effects of the late Paleozoic Alleghenian event, which signaled the end of the continental convergence, are not well known in Vermont. Folding and metamorphism from this event are better seen in the southern Appalachian belt and the coal bearing basins of southeast New England. Cretaceous igneous rocks of the White Mountain Igneous Suite (Barber Hill, Cuttingsville, and Ascutney) are some of the youngest rocks in Vermont.
See summaries of the:
Kaolin is found in a discontinuous 90 mile long belt extending along the Green Mountain front in western Vermont. Deposits occur near Pownal, Bennington, Shaftsbury, Dorset, South Wallingford, Tinmouth, North Clarendon, Rutland, Brandon, and Monkton. Weathering of Precambrian gneiss, and to a lesser extent the weathering of feldspathic and more clay rich layers of the Cheshire Quartzite, are offered as a possible hypothesis regarding formation of this belt. Hydrothermal replacement of the cement in the Cheshire Quartzite is an alternate generation method. Lenses of limonite and pyrolusite as well as minor occurrences of psilomelane and manganite, that probably represent different members of the parent rock, occur with the deposit and were mined for iron and manganese in the early 1900s.
The kaolin deposits from the Bennington-Shaftsbury area were actively mined and processed until the 1930s for use in the papers, pottery, fireclay and brick industries. The greatest production from this deposit, 11,000 tons, was mined by the Vermont Kaolin Corporation in 1930. The Brandon deposit yielded a total of 80,000 tons between 1902 and 1925.
The Monkton deposit, discovered in 1792, was first mined in the mid 1800s. The American Kaolin Company produced about 2,000 tons per year between 1883 and 1890. The deposit was later utilized for raw material for the Rutland Fire Clay Company from 1930 to 1944. In 1956, the deposit was purchased by Vermont Kaolin. Although core drilling and augering methods indicated the deposit would produce about 23 million tons, only 9,235 tons of clay were removed between 1956 and 1966, when the facility closed. The deposit had been mined by removal of the overburden with power shovel or dozer, with the mineral itself removed by power shovel or dragline. The kaolin in this deposit has high color variability and required a high degree of processing prior to use as a paper filler. Additionally, no efficient purifying method was available for the fine-grained graphite present in the formation during the period of active mining. As a result, continued mining at this location became economically unfeasible.
The sulfide occurrences in Vermont lie within the Connecticut Valley-Gaspe Synclinorium, the Bronson Hill Anticlinorium and the large Appalachian Province of stratabound massive sulfide deposits (Gair and Slack, 1979). In addition, isolated occurrences are found within the Green Mountain Anticlinorium Tectonic Province.
While a number of sulfide minerals are found in Vermont, including lead/zinc, copper, molybdenum and arsenopyrite, copper was the only mineral mined on a large scale.
No metallic minerals are currently being mined in Vermont. The Orange County copper district ores were discovered in 1793, with production beginning in the early 1830s. Until Michigan copper ores were discovered in 1846, Vermont was the chief copper producer in the United States. The Elizabeth Mine, located in South Strafford, was the nation’s largest copper mine until the Michigan deposits opened (Tillman, 1974). Vermont copper mines operated sporadically through the 1950s, and the closing of the Elizabeth Mine in 1958 brought an end to metal mining in Vermont. Ore minerals have not been exhausted in the Orange County copper district, but the ore grade is marginal and structural complexity makes mining extremely difficult (Ratte, 1982).
The Orange County district remains a scar on the surrounding landscape. The site is currently listed on CERCLIS, EPA’s database of potential hazardous waste sites, and will be addressed under the Superfund program. Strong environmental opposition is likely to deter future mining in the district unless it can be demonstrated that present day mining technology is capable of rehabilitating the landscape, including newly generated wastes and existing mining scars (Ratte, 1982).
Reports of gold being found in Vermont are on record from as early as 1845, when State Geologist C.B. Adams, in the “First Annual Report on the Geology of Vermont,” reported a find in Somerset, Vermont.
The California gold rush, which began four years later, enticed many Vermonters to search for gold outside their home state. During the mid-1850s, most of these gold hunters returned home. In 1849, Captain Abial Slayton, a Vermonter, struck it rich at a California gold claim. Upon his return to Vermont in 1855, Slayton found gold in what was then Hull’s Brook, now Gold Brook, in Stowe. Although he set up a sluicing operation employing several people, it never compared to the financial gain realized from the California claim. A tribute to Captain Slayton’s efforts was made in 1887 at the Mount Mansfield Electric Railroad, when the last spike to be driven was coated with Slayton’s gold.
In 1854, a mine of “gold, silver, lead and copper” was opened at Bridgewater, Vermont (Jackson, 1854). Gold was said to have been found there as small irregular grains in quartz. Dr. C.T. Jackson noted in 1867 that the great Appalachian gold belt passed through Plymouth and Bridgewater.
By the 1900s, however, it was determined that while gold was present in the state, it did not occur in paying quantities. Gold-bearing rocks in Plymouth and Bridgewater were mined, but the cost of getting the metal was far greater than the metal was worth. Dr. G.H. Perkins, Vermont State Geologist in 1900, stated “. . . it is therefore useless to spend time and money in trying to find a fortune in gold mining in Vermont. Considerable money has been lost because it was invested in such mining, but I have yet to hear of much that was made in this way in this state. Occasionally a little ‘pay dirt’ has been found, but in a short time the promising mine has been left unworked.” The mine shafts from these mining efforts can still be observed in Bridgewater and Plymouth.
Placer deposits were identified in the Plymouth area about 1855. Gold in the stream beds and the hillside gravels was probably derived from the denudation of gold-bearing quartz veins nearby. Surprisingly, gold derived in this manner has some commercial value, even though the original vein rocks do not constitute workable ore (Perry, 1929).
In spite of indications that no one will get rich looking for gold in Vermont, gold hunters still abound in the state. Every summer people converge on the gold-bearing rivers and streams, seeking to recover “free gold” from stream gravels.
ULTRAMAFIC ROCKS -
The ultramafic rocks are part of the Appalachian orogenic belt, which lies entirely within the crystalline rocks of the Appalachian Mountain system and represents slices of oceanic crust emplaced during continental collision. The ultramafic bodies, also known in geologic literature as ophiolites, consist of a central core of serpentinite surrounded by shells of talc-carbonate rock and steatite (Chidester, 1962).
The Bedrock Geologic Maps of Vermont (Doll, 1961; Ratcliffe and others, 2011) show the ultramafic belt extending the full length of the state with ultramafic bodies located in rocks of Cambrian and Ordovician age. Specifics of the ultramafic rocks of Vermont, asbestos, soapstone and talc, are discussed below.
Asbestos minerals are found in the serpentinized ultramafic bodies. The larger bodies are composed of central cores of massive dunite and peridotite which grade outward to massive or sheared serpentinite. Chrysotile asbestos occurs as cross-fiber veins in the more massive portions of the ultramafic bodies and as slip-fibers in the highly sheared serpentinites (Ratte, 1982).
Asbestos was first discovered about 1824 by lumbermen working on Belvidere Mountain. Small prospects continued to be worked for a century. In 1901, the first company to mine asbestos, New England Asbestos Mining and Milling Company, organized with the purpose of exploring what was then called Cotton Rock in Eden, Vermont. Prior to the company’s organization, most asbestos was mined and milled in Canada.
The Ruberoid Company bought the Belvidere Mountain mine in 1936. By this time, the Eden mine was the only operating chrysotile asbestos mine in the country, encompassing 1700 acres of asbestos deposits on Belvidere Mountain. When Ruberoid took over, the first modern, large scale development began (Crane, 1954). In 1967, the company merged with General Aniline and Film Corporation and became known as GAF Corporation.
By 1973, health issues regarding the mining and use of asbestos came into public focus. Only two years later, GAF announced that the Eden mine would cease its operations. An economic feasibility study had determined that the estimated $1 million cost to retrofit the plant for the required environmental dust control equipment made further operation of the mine unprofitable (Wallace, 1990).
That same year, mine workers raised $2 million and took control of the plant from GAF (Clairborne, 1976). The new company was called the Vermont Asbestos Group (VAG). The serpentine is blasted loose from the quarry face and then trucked to the mill where the fibers are separated from the rock. Vermont ranked second in the manufacturing of asbestos to California, the only other state that produces asbestos. (Note 2005: The mine closed in 1993. Asbestos mining no longer occurs in Vermont.)
Like asbestos mineralization, talc (and its massive variation called soapstone) is associated with serpentinized ultramafic bodies.
Commercial use of soapstone began in Vermont around 1825 when water pipes, two and three feet long, were cut from three and four inch blocks of soapstone bored hollow. The finished pipe sold at a mere six cents per foot. By the late 1800s the largest soapstone quarries in the nation were located at Grafton, Vermont and Franconia, New Hampshire (Haig, 1963).
The properties of soapstone (heat absorption and retention and softness) allowed it to be worked easily, making it popular for fireplace hearths, stoves, foot warmers and griddles, as well as for sinks and door sills.
Soapstone was produced at nearly every talc mine in the state, but is now only produced intermittently at one quarry in Chester.
Talc is associated with serpentinized ultramafic bodies that are found sporadically in a north-south trending belt. The ultramafic bodies containing talc (steatite) are composed of a central core of serpentinite surrounded by a shell of talc-carbonate rock and followed by an outer shell of talc (steatite). Unlike granite and marble, talc exists in ore form and therefore must be processed before pure talc may be produced (Orton, 1952). Talc in Vermont occurs as metasomatically altered serpentine bodies with a talc content of 48-55 percent surrounded by a 20 foot rim of high talc content ore.
Cyprus Industrial Minerals Company currently operates ten talc mines in the state. These include North Windham (inactive), Hamm, Troy, Hammondsville (inactive), Black Bear, Rainbow, Argonaut, Clifton, Frostbite (inactive), and the Newfane Quarry (inactive). Conventional drill and blast techniques are used to remove the ore. There are four Cyprus mills in the state which produce industrial grade talc for inert fillers as well as cosmetic talc. (Note 2005: Talc mines and mills are owned by Imerys Talc; the Argonaut Mine is the only operating talc mine in Vermont)
Vermont ranks second in output among the ten states that produce talc. (Note 2005: Vermont ranked #3 of six states in talc production in 2004)
The history of Vermont’s mineral industries reveals numerous efforts over two centuries to extract and market the state’s economic minerals. The success of these efforts has varied, and many of the commodities once quarried and processed in the state are no longer under production.
Vermont’s remaining mineral industries, however, continue to play a significant role in the local and state economy. For the most part, these industries owe their stability to controlled growth, innovative quarrying, mining and milling techniques, and sound environmental management. (Note 2005: Total value of non-fuel mineral production, including sand and gravel, in 2003 was $73,000,000)
Baldwin, Brewster, 1977, Notes on the Geology of Vermont, an Ancient Continental Margin, Middlebury College.
Chidester, A.H., 1962, Petrology and geochemistry of selected talc-bearing ultramafic rocks and adjacent country rocks in north-central Vermont, US Geological Survey, Prof. Paper #345, 207 pgs.
Clairborne, W.L., 1976, Vermont Asbestos Group: Worker-owned mine shows bright prospects, Vermont Life, vol. 30, #3, pgs 9-13.
Crane, C.E., 1954, Vermont makes silk from stone – the story of the nation’s largest asbestos operation located on a remote mountainside of northern Vermont, Vermont Life, vol. 8, #3, pgs 2-9.
Doll, C.G., 1961, Centennial Geologic Map of Vermont, Vermont Geological Survey, scale 1:250,000.
Gair, J.E., and Slack, J.F., 1979, Map showing lithostratigraphic and structural setting of stratabound (massive) sulfide deposits of the US Appalachians, US Geological Survey, open-file report OF-79-1517, 4 sheets.
Haig, George, 1963, Slick, hot and handy (soapstone), Vermont Life, vol. 18, #2, pgs 13-14.
Jackson, C.T., 1854, On a recent mine of gold, silver, lead and copper recently opened at Bridgewater, Vermont, Boston Society Natural History Proc., vol. 5, p. 62.
Orton, Vrest, 1952, Talcum powder under our mountains: The story of Vermont’s Eastern Magnesia Talc Company, one of the largest talc operations in the world, Vermont Life, vol. 6, #2, pgs 34-41.
Perkins, G.H., 1900, Report of the State Geologist on the mineral resources of Vermont (1899-1900), Burlington, VT, Free Press Association, pgs 12-14.
Perry, E.L., 1929, Geology of Bridgewater and Plymouth townships, Vermont, Vermont State Geologist, 16th Report (1927-1928), pgs 62-63.
Peterson, E.L., 1967, Vermont – Sources of Aluminum: Potential Sources of Aluminum, US Bureau of Mines Information Circular IC-8335, pgs 123-133.
Ratte, C.A., 1982, Mineral resource provinces of Vermont, Vermont Geological Survey, open-file report 1982-1, 45 pgs, 1 map.
Tillman, D.A., 1974, Mining in Vermont, Tower Publishing Co., Portland, ME, 102 pgs.
Wallace, Paulette, 1990, Eden asbestos mine among first in United States, News and Citizen, Morrisville, VT, February 22, 1990.