The prison and mine
buildings are currently closed for
restoration!
Click
here for more information!
Please note: you can still gain credit for the activities by
carefully reading the write-up and taking a photo of the
plaque!
Old Newgate Mine
Quick description: In the early eighteenth century the
need for metal resources by the colonists lead to the opening of
several copper prospects in the Connecticut River Valley. Copper
was first discovered in the Newgate area in 1705. Several attempts
were organized to exploit the deposit, but none proved especially
profitable. The tunnels that were driven into the rock were used as
a prison during the Revolutionary War. It was then that the name
New-Gate was applied, perhaps to remind British captives of the
infamous British prison. At this Earthcache you can explore some of
the mine workings. The park website is:
http://www.chc.state.ct.us/old_new.htm
.
Purpose: This EarthCache is created by the Connecticut
Geological and Natural History Survey of the Department of
Environmental Protection. This is one in a series of EarthCache
sites designed to promote an understanding of the geological and
biological wealth of the State of Connecticut.
Directions: Take exit 40 off I-91, heading West on Rt.
20. Proceed for approx. 8 miles until you come to the intersection
of Rt. 187 & 20. Continue up the hill, take a right at the
signal light. Head North on Newgate Road for 1 mile, Old
Newgate Prison is on the left.
Please note, visitors hours, days open and admission fees are
subject to change.
The park is seasonal, that is it is only open from May 1 to
October 31. It is closed Monday through Thursday. There is an
entrance fee. The mine is not wheel-chair accessible because of
stairs and slanting walkways. The mine tour may be difficult for
those with any ambulatory handicap
Address: 115 Newgate Road, East Granby, CT
Phone: 860.653.3563
Hours: May-Oct., Fri - Sun 10 am - 4:00 pm
Current Admission Prices: adults $10, seniors (60+) & college
students with ID $8, children (6-17) $6, children under 6 are
free.
Geologic background information. Copper minerals in
central Connecticut occur within particular layers of sedimentary
rock or in veins that cut across the layering. Newgate deposit is
of the former type and is referred to as a strata-bound deposit.
The sulfide minerals bornite, Cu5FeS4, and
chalcopyrite, CuFeS2, partially replaced by chalcocite,
Cu2S, are the principal ore minerals. An ore mineral is
any mineral that contains a useable element in a chemical form that
is easy to purify. Metal-bearing sulfide minerals are easy to
purify by smelting in an oxidizing environment. The bornite and
chalcopyrite are difficult to spot in the mine because of their
scarcity (they were most all removed by mining activities) and the
dim lighting (they are both dark colored). They were disseminated
in grey sandstones at or about the stratigraphic level of the
Talcott Basalt. Brightly colored malachite
Cu2(CO3)(OH)2 and cuprite,
Cu2O, are more conspicuous but are clearly secondary
after the primary ore minerals. They are easily seen in the
mine.
More than 200 million years ago (during the Mesozoic Era) sand
and mud (which later hardened to sandstone and shale) were
deposited by prehistoric streams that flowed across this area of
Connecticut. When originally formed, the layers of sand and mud
were nearly horizontal. Significant tilting of the layers occurred
several millions of years later. Today the mine floor and ceiling
slope at about 20o following the strike and dip (tilt)
of the ore layer. 
Mineralization of the sandstone occurred before the rock was
buried deeply enough to compact it. Iron-rich dolomite (ankerite),
recognizable by its rusty weathering, precipitated first from
groundwater that percolated through the rock. Later, copper-bearing
sulfur-rich solutions of hot saline-water migrated through the
sandstone and deposited the primary ore minerals, bornite and
chalcopyrite or chalcocite Later still, copper was leached from the
ore and deposited as malachite and cuprite.
EarthCache ACTIVITY 1. The coordinates given at
the beginning of this cache are for a location outside the walls of
the prison that may be visited at any time of year. It is next to a
plaque built by the New-Gate Friends. To log your visit to this
Earthcache send a picture of yourself and your GPS unit showing the
plaque and view to the west.
From that point one may see across the valley and past Manitook
Mountain to the hills west of the Mesozoic-aged Hartford Basin.
Three lines of hills may be distinguished. The low tree-covered
hills in the foreground are underlain by sedimentary rocks of the
New Haven Arkose that are Triassic in age. The hills in the middle
ground, Manitook Mountain directly west and the Barn-door Hills to
the southwest, are the western trap-rock hills of the Hartford
Basin. They are part of the Jurassic aged intrusive igneous rocks
and are composed of diabase and basalt. They were intruded at the
beginning of the Jurassic Period as part of the igneous event that
formed the lava flows of the Talcott Basalt. The mineralizing
fluids may have been in part heated by these intrusive rocks. The
hills in the distant background that form the skyline are underlain
by Paleozoic metamorphic rocks. A fault is found at the base of
those hills.
Looking behind you toward the east one sees the imposing cliffs
held up by the Holyoke Basalt a lava flow that is younger than both
the Talcott Basalt and the grey mineralized sandstones at Newgate.
It is more likely that the mineralizing fluids were heated in
association with the Holyoke igneous event.
When the park is open you may gain entrance for a modest
admission fee that is used to maintain the park. Inside is a small
museum and several buildings. On the grounds you may see the
remains of a smelting furnace.
EarthCache activity 2. The mine entrance is
located at N. 41o57.73’, W. 072o
44.72’. Go into the mine. On your left at the bottom of the
stairway entrance is some of the ore. The ore minerals are
disseminated in a grey sandstone. Here there are two minerals that
are easily seen: ankerite Ca(FeMgMn)(CO3)2
and malachite. What color is the malachite? Hint:
Information about recognizing the iron-rich dolomite may be found
in preceeding narrative.
Malachite is the easiest ore mineral to spot in the mine. That
is because of its distinctive color and the fact that is usually
found with Fe-dolomite (also easy to spot). It may be found along
the walls of the mine and further into the mine, on the ceiling and
in
&
pillars of rock left to help support the ceiling. Obviously, most
of the richest concentrations of ore minerals were removed by the
mining activity. The concentration of the ore that was removed
averaged 12% copper; what was left behind contains between 2.5 and
10% copper. In addition, up to 10 oz./ton of silver was found.
Copper averages less than 1% in most of the grey beds. Uranium
minerals have also been identified in the mine.
Much of the mine is flooded. It was pumped several years ago
revealing hundreds of feet of tunnel along which little or no
mineralization was found. That part of the mine workings has since
reflooded and may be seen at deepest part of the accessible mine.
The water level in the mine is equal to the groundwater level in
nearby water wells. About half of the mine above the water table,
i.e. not flooded, is not accessible because of safety
concerns. They are roped off and should not be entered.
The State Geological and Natural History Survey of Connecticut
put together this EarthCache for your enjoyment and your continuing
awareness of Connecticut geology.
Additional information:
Bell, Michael, 1985, The Face of Connecticut. State
Geological and Natural History Survey
of Connecticut, Bull. 110, 196p.
Gray, N.H., 1982, Copper occurrences in the Hartford Basin of
northern Connecticut, in
Guidebook for Fieldtrips in Connecticut and southern
Massachusetts; New England Intercollegiate Geological Conference,
74th Annual Meeting; State Geological and Natural
History Survey of Connecticut, Guidebook #5, p. 195-211.
McHone, J.G., 2004, Connecticut in the Mesozoic World.
State Geological and Natural
History Survey of Connecticut, Spec. Pub. #1, 40p.
How do people log this EarthCache? To log your visit to
this EarthCache send a picture of yourself and your GPS unit
showing the plaque and view to the west and send your answer to the
question for activity 2 to the cache owner.
Difficulty: 1
Terrain: 2 because of stairs and steep slopes inside the
mine.
Type of land: State Historical Park
EarthCache category: mine; ore deposit.