COMPARING THE EMPLACEMENT CONDITIONS OF TWO MINERAL DEPOSITS IN WESTERN CONNECTICUT

This study aims to analyze fluid inclusion data from two different quartz veins that are 10 km apart in western Connecticut. Inclusion data will be used to determine the pressure-temperature (P-T) conditions under which the veins formed and to assess whether or not a genetic relationship exists. The first study area is The Mine Hill Quarry in Roxbury, CT. Once a major supplier of iron in the region, the mine worked a 2-3 m thick siderite-bearing quartz vein hosted in granitic gneiss. The vein also contained sparse amounts of galena. Stable isotope analysis of the siderite returned δ¹⁸O values of -16.3 to -13.4 and δ¹³C values of -11.4 to -9.6, aligning with a hydrothermal origin. Lead-lead dating of the galena resulted in δ₂₀₇Pb/δ2₀₆Pb values of 0.842 and δ²⁰⁶Pb/δ²⁰⁴Pb values of 18.641, pointing to an origin of 135-140 Mya late during Mesozoic rifting. The second study area is in the Hidden Valley Preserve (HVP) in Washington, CT. Here, an undocumented quarry once worked an amphibolite-hosted quartz vein that is 3m thick. The vein only contains quartz and has a strike of 020° and an eastward dip of 10-15°. No stable isotope analysis was conducted at this location. Six quartz specimens from each site were evaluated using microthermometry techniques, and 76 usable fluid inclusion data points were obtained. Data included both two-phase H₂O-NaCl and three-phase H₂O-NaCl-CO₂ inclusions. Timing of fluid inclusion formation with respect to vein formation is difficult to ascertain and they are classified as undifferentiated. P-T conditions of fluid trapping were calculated assuming a geotherm of 50-80°C. For the HPV two-phase inclusions, P-T conditions range from 125-200°C at 35-90 MPa for lithostatic conditions and 115-175°C at 15-30 MPa for hydrostatic conditions. HPV three-phase data resulted in P-T conditions of 140-305°C at 40-150 MPa for lithostatic conditions and 120-210°C at 5-35 MPa for hydrostatic conditions. Roxbury two-phase data indicates P-T conditions of 310-630°C at 100-280 MPa for lithostatic conditions and 260-365°C at 30-65 MPa. No three-phase data was obtained for this location due to inclusion decrepitation. Our results suggest that the HVP and Roxbury quartz veins do not share a common origin and that the HVP vein was subject to multiple fluid trapping events.