Geology of the Hammer Down mesothermal gold deposit, Newfoundland Appalachians, Canada

• Published in: Canadian Journal of Earth Sciences
• Main Authors: Gaboury, Damien, Dubé, Benoît, Laflèche, Marc R., Lauzière, Kathleen
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1996
• Subjects: General Earth and Planetary Sciences; Canada; Newfoundland
• Online Access: http://dx.doi.org/10.1139/e96-025; http://www.nrcresearchpress.com/doi/pdf/10.1139/e96-025

The Hammer Down gold deposit is one of the most significant mesothermal vein-type gold deposits in the Canadian Appalachians. It is located within a complex sequence of Ordovician, mafic-dominated tholeiitic and calc-alkalic and arc-related volcanic rocks, which was intruded by Silurian felsic porphyry dykes. The host rocks have undergone complex polyphase deformation. At least three deformational events influenced vein emplacement and overall geometry of the deposit. A Taconian deformation (D 1–2 ) was responsible for the development of a 250 m wide zone of high-strain deformation (HSZ 1 ) at the interface between two blocks of Ordovician rocks: the Catcher's Pond Group and the Lush's Bight Group. Rocks included within the HSZ 1 , represent "exotic" slabs of volcanic rocks that were tectonically juxtaposed, intensively foliated (S 1 ), and folded (F 2 ). Gold occurs in high-grade, sulfide-rich, fault-fill quartz veins that occur within the HSZ 1 . At the outcrop scale, these veins are hosted by discrete centimetre- to metre-wide ductile–brittle D 3 high-strain zones (HSZ 3 ) of Silurian or younger age. The development of the gold-hosting structures (HSZ 3 ) is genetically related to layer anisotropy induced by intrafolial F 2 folds, and most importantly by the presence of felsic porphyry dykes, which were competent compared to the intensively foliated and incompetent mafic volcanic rock sequence. A postmineralization D 4–5 deformation, which included two generations of folds (F 4 and F 5 ) and late brittle faulting, is responsible for the actual geometry of the deposit.