ECONOMIC GEOLOGY OF THE TRIASSIC-JURASSIC AGE 
HARTFORD FAILED-RIFT BASIN, SOUTHERN NEW 
ENGLAND

	ALTAMURA, R.J.1, Department of Geosciences, The 	
		Pennsylvania State University, University Park, PA 
		16802

Earliest organized mining of rock of the Hartford basin was in 1689 
for building stone.  Redbeds (red and brown arkosic sandstones) were 
excavated for use as dimension stone during the period from 1689 to 
present with a heyday in the mid- to late 19th century.  C.U. Shepard 
in his 1837 economic geology survey of Connecticut, reported an 
annual production of 500 tons of processed lime from a 30 - 45 cm 
thick limestone beds in quarries located  in marly shales of the Shuttle 
Meadow Formation adjacent to the Talcott flow near the 
Berlin/Southington, CT town lines.  P.D. Krynine stratigraphically 
correlated this limestone deposit with another in North Branford, CT 
that was also excavated for lime.  These limestone beds are up to 5-m 
thick, and also occur at the base of the Shuttle Meadow Formation.  
These beds are finely banded (0.5 - 3 cm), the bedding planes being 
marked by an accumulation of mica flakes.  At the type locality at the 
Coe's quarry, the beds are 4-m thick.  At least a portion of the unit has 
recently been reinterpreted to be metasomatically altered basalt.
	Tholeiitic basalt has been quarried in the basin for some time 
for use as road metal and aggregate.  Most of the production has been 
from basalt that was excavated in the Hartford and Pomperaug basins.  
Sedimentary and igneous rocks of the Newark Supergroup were 
excavated for utilitarian commodities, such as building stone, lime, 
and trap rock that were made available to a developing population.
	Other economic deposits associated with the Hartford rift are 
those classified as hydrothermal in origin.  Recent work on the 
Lantern Hill silicified fault near North Stonington, CT indicates that 
faulting and hydrothermal fluid activity associated the rifting of 
Pangea in southern New England began in the Middle Triassic prior to 
deposition of the first Newark Supergroup sediments (i.e. the Late 
Triassic New Haven Arkose) into the basin.  These early normal faults 
appear to have been dominated by hydrothermal fluids that contained 
mostly dissolved silica.  Several silicified zones similar to Lantern 
Hill occur in the footwall of the eastern border fault (EBF) of the 
Hartford rift and to the east, but not on the west side of the rift.  The 
Mesozoic quartz was excavated at Lantern Hill for use as filtration 
medium and industrial sand.  Typical annual sales of the quartz at 
Lantern Hill were approximately 3 million dollars at the time of the 
closing of the operation in 1994.
	Later in the evolution of the rift basin, during the eruption of 
flood basalts, copper was deposited in stratiform deposits in the 
Shuttle Meadow Formation beneath the massive Holyoke Basalt.  
Chalcopyrite and bornite were excavated here during colonial times at 
copper mines near Simbury, Connecticut.  Their origin has been 
interpreted to have been associated with circulating fluids driven by 
heat associated with emplacement of the Holyoke flow.  Barite occurs 
in veins that like the copper are inferred by many to have originated 
from basaltic melts emplaced into the sedimentary stack.  Copper was 
mined in the 19th century along the western border of the rift near 
Bristol, CT and along the EBF in Manchester, CT.  Vein barite and 
galena occur in many places in the basin, emplaced in redbeds and 
basalts.  Significant mining occurred in the 19th century at Loudville, 
MA, where veins emplaced along border faults produced 12.5 ounces 
of silver per ton of processed galena.  Argentiferous galena was also 
mined from veins along the EBF near Middletown, CT.  Origin of 
these hydrothermal deposits was apparently not associated with local 
emplacement of basaltic melts and a basin-wide circulation system is 
envisaged.
	Exploration for oil had been conducted in the Pomperaug 
basin around 1890, a drill hole was spudded in the Hartford basin near 
the village of Forestville, CT, and in the mid-1980's Texaco ran 
seismic traverses along and across the Hartford basin as part of a 
modern exploratory program.  It is not uncommon to find bitumen in 
these rocks.  Coal is reported to have been excavated in the 19th 
century near the towns of Berlin and Windsor.

1Present Address: Dept. of Geology & Planetary Sciences, University 
of Pittsburg, Johnstown, PA  15904