Stratigraphy, Structure, and Geochemistry of the Halfmile Lake Massive-Sulfide Deposit, New Brunswick

Abstract The Halfmile Lake stratiform volcanogenic massive-sulfide deposit consists of pyrrhotite-rich breccia-matrix sulfides and pyrite-pyrrhotite-rich layered sulfides that form a laterally continuous sheet stratigraphically underlain by an extensive pyrrhotite-chalcopyrite-quartz stringer zone. Mineralization is hosted by a sequence of felsic pyroclastics and volcanic-derived, fine-grained metasediments. The proportion of volcanic to sedimentary rocks indicates increasing vent proximity from southwest to northeast across the deposit area. Fine- to medium-grained felsic pyroclastics and roughly equal amounts of fine-grained metasediments comprise the stratigraphic footwall to the mineralization. Quartz-feldspar porphyritic bodies cut this sequence and may have provided the heat source for exhalite activity. Felsic tuffs, locally crystal-rich, and lesser amounts of metasedimentary rocks make up the immediate stratigraphic hanging wall. This sequence is stratigraphically overlain and locally interfingered with mafic volcanics that contain substantial proportions of felsic fragments. Deposition of sulfides post-dated the beginning of felsic volcanism, which places the deposit in the middle of the Lower Tetagouche Group. Compositions of the volcanic rocks range from basalt to rhyolite and exhibit sub-alkaline affinities. Strongly overprinted whole-rock, trace-element, and REE geochemical signatures resulting from mineralizing hydrothermal activity confirm the genetic relationship between the stringer zone and the mineralized sheet. Large-scale D, folding has overturned the entire sequence. D, thrust faults and related sheath-like folds have profoundly affected sulfide distribution. D2 is manifested by a penetrative 82 foliation, and D3 is represented by large-scale open folds.
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Summary: The Zn-Pb-Cu-Ag ore deposits of the Boundary and N-5 zones near Bathurst, New Brunswick, occur in a polydeformed volcano-sedimentary sequence that is part of the Ordovician Tetagouche Group. Massive and disseminated sulfides are hosted by an argillaceous to cherty sedimentary sequence that is stratigraphically underlain by a siliceous fragmental unit and is overlain by a feldspar-rich crystal tuff and related tuffaceous rocks. The deposits have a low iron sulfide content relative to that of...
Publication: Exploration & Mining Geology
Author(s): ART HAMILTON
Issue: 2
Volume: 1
Year: 1992
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Summary: The Key Tuffite is a thick (0.3 m to 6 m) and laterally extensive (—10 km) cherty, sulfide-bearing tuff unit in Archean greenstones in the Matagami mining district in northwestern Quebec. It lies at the contact of the Watson Lake Group and overlying Wabassee Group volcanic rocks, and is host to major Zn-Cu volcanogenic massive sulfide deposits. The tuff component is highly altered and its volcanic precursors are not identifiable by petrographic means. The tuff is mixed with a volcanic...
Publication: Exploration & Mining Geology
Author(s): S. LIAGHAT, W.H. MacLEAN
Issue: 2
Volume: 1
Year: 1992
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Summary: The Murray Brook massive sulfide deposit, which was the first geochemical discovery in the Bathurst camp, is one of the largest sulfide deposits in the area. The massive sulfides are hosted by quartzose metasedimentary rocks in the lower part of the Ordovician Tetagouche Group. This thick succession of sedimentary rocks is overlain conformably by felsic volcanic rocks, and is structurally overlain by mafic volcanic rocks. The massive-sulfide body is porydeformed, but primary metal zoning is...
Publication: Exploration & Mining Geology
Author(s): M. P. RENNICK
Issue: 2
Volume: 1
Year: 1992
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Summary: The volcanic-dominated Tetagouche Group in northern New Brunswick contains numer ous massive-sulfide deposits and intimately associated metalliferous sediments. The massive sulfides i: are generally hosted by Llanvirnian-Llandeilian volcaniclastic sedimentary rocks of the Nepisiguit ; Falls, Patrick Brook, and Boucher Brook formations. These formations are intercalated or closely associated with rhyolitic-dacitic flows and/or domes, and minor continental tholeiites of the Flat Landing Brook...
Publication: Exploration & Mining Geology
Author(s): CEES R. VANSTAAL, LESLIE R. FYFFE, JOHN P. LANGTON, STEVE R. McCUTCHEON
Issue: 2
Volume: 1
Year: 1992
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Summary: The "Brunswick Horizon" an informally named ore-bearing unit near the top of the Nepisiguit Falls Formation in the Ordovician Tetagouche Group, hosts the Brunswick No. 6 and No. 12 base-metal mines, as well as the former Austin Brook iron mine, in northern New Brunswick. Detailed structural analysis of the No. 6 and No. 12 mines led to the prediction that a massive-sulfide deposit may have been repeated by F, folding along the Brunswick Horizon. A subsequent drilling program discovered the...
Publication: Exploration & Mining Geology
Author(s): J.J. HUSSEY
Issue: 2
Volume: 1
Year: 1992
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Summary: The Captain North Extension deposit consists of five sulfide lenses hosted in cherty and chloritic metasediment that is bounded by quartz-eye rhyolite and laminated rhyolite. Lens 2 consists of sphalerite and galena with silver-rich tetrahedrite in chert. Lens 3 contains massive pyrite, with chalcopyrite and minor gold, gradational to minor pyrite in a chloritic metasediment. The other lenses are unexplored. The sulfides occur as beds, fracture infills, and disseminated grains. Reserves are...
Publication: Exploration & Mining Geology
Author(s): K.D.A. WHALEY
Issue: 2
Volume: 1
Year: 1992
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Summary: Brunswick No. 12 is a vent-proximal massive sulfide deposit that formed above a feeder pipe with associated hydrothermal alteration. Because of the replacement of bedded sulfides deposited above the hydrothermal vent, individual sulfide lenses show the following vertical and lateral zoning outward from the vent complex: massive pyrite-pyrrhotite-chalcopyrite core interlayered pyrite-sphalerite-galena (Pb-Zn ore zone) — bedded pyrite. The feeder zone which underlies the Cu-rich core consists...
Publication: Exploration & Mining Geology
Author(s): WILLIAM M. LUFF, WAYNE D. GOODFELLOW
Issue: 2
Volume: 1
Year: 1992
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Summary: The Bathurst-Newcastle district, a subcircular area approximately 50 km in diameter, contains 37 massive-sulfide Zn-Pb-Cu deposits that have defined tonnages, and has 58 additional significant occurrences. The largest deposit is Brunswick No. 12, with total reserves (including past production) of 148 million tonnes grading about 12.5% combined Pb-Zn. The deposits/ occurrences are spatially associated with a felsic volcanic pile that contains a significant sedimentary component. In the...
Publication: Exploration & Mining Geology
Author(s): STEVEN R. McCUTCHEON
Issue: 2
Volume: 1
Year: 1992
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