Abstract

A variety of mineral deposits were formed during the tectonic evolution of the Mascarene-Nerepis and Rolling Dam Belts, in southwestern New Brunswick. The Mascarene-Nerepis Belt is mainly underlain by intensely deformed Upper Silurian to Lower Devonian andesitic and rhyolitic volcanic rocks with interbedded calcareous siltstone and slate. The Rolling Dam Belt consists largely of Ordovician graphitic slate overlain by Upper Silurian to Lower Devonian greywacke and slate.During Middle Devonian time, both belts underwent polyphase deformation and a large batholith composed mainly of granite and related plutonic rocks was emplaced (Acadian orogeny). Base metal deposits designated as early tectonic in this report occupy dilatant structures related to group 3 folds, along the margins of these plutons. In the Mascarene-Nerepis Belt, base metal deposits occur in andesite and rhyolite tuffs, and calcareous pelitic sedimentary rocks deformed by these structures. Gold-arseno-pyrite-quartz veins occupy similar structures in graphitic slate of the Rolling Dam Belt.A few early tectonic deposits occur in plutonic rocks. Nickel-copper sulfides occur as massive bodies and disseminated blebs in a mafic pluton in the St. Stephen area (Rolling Dam Belt). Tungsten-bearing greisen veins occur in granitic rocks of the Square Lake area (Mascarene-Nerepis Belt).The second major orogeny, which occurred during the Carboniferous, is generally characterized by open folding, and wrench- and block-faulting. Volcanism was active in the Mount Pleasant area (Rolling Dam Belt) and numerous small intrusions were locally emplaced in both belts Molybdenum-copper, tungsten-molybdenum-bismuth, tin- and silver-base metal sulfide deposits, which were formed during this period, represent the late tectonic metallization episodes in both belts.

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