INTRUSION-RELATED GOLD MINERALIZATION IN SOUTHWESTERN NEW BRUNSWICK: THE MAIN ZONE, CLARENCE STREAM GOLD DEPOSIT

The Clarence Stream gold deposit is situated immediately southeast of the Sawyer Brook Fault, which is interpreted to be the surface expression of the boundary separating the Gander Zone to the northwest from the New River terrane to the southeast. Gold-bearing quartz veins are structurally controlled in a northeast-trending, brittle-ductile shear zone within the contact aureole of the I-type Magaguadavic phase of the Late Silurian to Devonian Saint George Batholith. This shear zone, which is likely a splay of the Sawyer Brook Fault, cuts a Silurian volcanosedimentary sequence of the Waweig Formation, and is occupied by multiple dykes of the East Branch Brook gabbro. Geochemical analysis and Th-U-Pb dating of auriferous granitic dykes that intrude the shear zone are consistent with their derivation from the Magaguadavic Granite as late fractionates.

The metal assemblage, characterized by a Au-As-Sb signature, primarily consists of arsenopyrite, pyrrhotite, berthierite, and sphalerite. Gold is mainly associated with berthierite as native gold grains and aurostibite. Based on paragenetic studies and sulfide phase equilibria, the temperature range of the deposit is estimated to be ~£ 360ºC at a sulfur activity of £ -8.

An isotopic signature of the mineralizing fluid was calculated to range between d¹⁸O=6.0 to 6.6 ‰ (analyses of mineralized quartz veins) and dD=-50.6 to -74.9 ‰ (whole-rock analyses). Common Pb isotopic signatures of mineralized quartz vein samples (n=4) have values of ²⁰⁶Pb/²⁰⁴Pb=18.28-18.48, ²⁰⁷Pb/²⁰⁴Pb=15.59-15.77, and ²⁰⁸Pb/²⁰⁴Pb=38.20-38.57, which overlap reported values for the Magaguadavic Granite. Measured d³⁴S values from mineralized quartz vein and pegmatite samples (n=15) clustered tightly within the range of –1.6 to 3.0 ‰. These results are consistent with a magmatic source.

Isotopic, geochemical, and geochronological evidence substantiate the intrusion-related genetic model initially proposed for this deposit. This evidence has established a genetic link between the gold mineralization and the nearby Magaguadavic Granite.