Paper No. 8
Presentation Time: 8:00 AM-12:05 PM
FIELD RELATIONS, PETROGRAPHY AND GEOCHEMISTRY OF LAMPROPHYRE DIKES, TORRINGTON, CT
West of Torrington, Connecticut, in the Litchfield Hills, a continuation of the Berkshire and Green Mountains of western Massachusetts and Vermont, a variety of small to large granitic to ultrabasic intrusions were emplaced along a major tectonic line, the Hartland- Waramaug Fault. One of two major faults running along the junction of the proto- North American continent ( early Paleozoic and Proterozoic) and the Iapetos or old oceanic terrane (early to middle Paleozoic), the Hartland-Waramaug Fault separates the Hartland Fm. granulites and muscovite-quartz schists from the Waramaug Fm. quartz-plagioclase-biotite gneiss. Lamprophyre dikes have been recorded in the Hartland granulite and in the younger Hodges Mafic Complex; the latter is host to the Hodges nickel prospect, mined for nickel, cobalt and copper sulfides as far back as the mid-1700s.
The deposit, located along Nickel Mine Brook in West Torrington, CT, occurs at a local fold in the NE-trending fault (Gates and Christensen, 1965). The Hodges Mafic Complex is characterized by a fine to medium grained amphibolite with hornblende and plagioclase as major components, with subordinate biotite and quartz. Gneiss and intermixed hornblende gabbro and amphibolite are present in the vicinity of the complex. Glacial sediment (till) covers a large area and is very common in the Besse Park area, the site of a more intermediate, biotite-rich (and nickel sulfide-free) lamprophyre dike in the Hartland Formation.
Samples from the two areas (Besse Hill and Hodges Nickel prospect) were collected in the fall of 2009. Samples were thin-sectioned for transmitted light petrography; polished samples of the nickel prospect for reflective light petrography. Select samples will be analyzed for major and trace element chemistry using X-Ray fluorescence.