Epithermal deposits form at relatively shallow crustal depths from low temperature fluids that are convectively circulated through host rocks by heat related to nearby subvolcanic intrusions. Large zoned alteration haloes (created over areas from 1 to >100 m laterally) are characteristic of this deposit type and are key to honing in on the mineralized areas of a hydrothermal system (Hedenquist 1987). Epithermal deposits are generally formed in an extensional volcanic arc environment. In some cases, these deposits may overlie sizable porphyry copper deposits. Typically, they have a metal assemblage consisting of gold, silver , copper , and arsenic (Sillitoe and Hedenquist 2003). The majority of the native gold mineralization occurs with pyrite in irregularly shaped quartz-flooded zones, breccia zones, or pipes associated with steeply dipping faults at the core of these systems (Simmons et al. 2005). Veins located near the lower limits of these deposits are generally enriched in base metals and silver with minimal quantities of quartz whereas the veins located in the upper portions of the system tend to be wider and are gold- and quartz-rich.
The Chambers Settlement occurrence , located east of Sussex, is an example of an epithermal gold system. The old shaft and adit at the former Watson Silver Mine are still visible in the vicinity of the occurrence. An intense alteration zone, hosted by Neoproterozoic volcanic rocks, typically includes such minerals as quartz, pyrophyllite, kaolinite, topaz, alunite, and specularite. Highly siliceous sericitic, pyrite-rich rocks collected from the area surrounding the old adit yielded approximately 1 g/t gold.
New Brunswick’s geological diversity has provided favourable conditions for the generation of several types of gold deposits in this part of the Appalachian Orogen. The majority of these deposits were formed in response to two main geological events:
(1) when the Iapetus ocean basin, volcanic arcs, and back-arc basins were opening during the Neoproterozoic to early Paleozoic (Cambrian to Ordovician); and
(2) when the ocean closed, and deformation, uplift, and juxtaposition of various tectonic blocks took place later in the Paleozoic (Silurian to Permian).
Only minor epithermal gold mineralization has been found associated with arc-related Neoproterozoic volcanic rocks. Gold-rich volcanic massive sulphide (VMS) deposits were deposited during the Ordovician in a back-arc basin environment. Later , orogenic gold deposits were formed and focussed along major fault structures related to ocean closure and development of accretionary complexes spanning Silurian to Permian time. Intrusion-related and skarn gold deposits were generated along with the large volumes of post-orogenic magma mainly during the Late Silurian to Early Devonian, while porphyry gold mineralization is found in both Ordovician and Devonian plutons. Some relatively minor paleoplacer gold occurrences, formed during erosion of the Appalachian mountain chain in the Late Carboniferous, may exist in the younger sedimentary rocks that cover much of eastern New Brunswick.