scholarly journals Sulfur Isotope Ratios from VMS Deposits in the Penokean Volcanic Belt, Great Lakes Region, USA: Constraints on the Source of Sulfur in a Paleoproterozoic Intra-Arc Rift

Minerals ◽  
2018 ◽  
Vol 9 (1) ◽  
pp. 6
Author(s):  
Nicholas Moleski ◽  
Anthony Boxleiter ◽  
Joyashish Thakurta
Keyword(s):  
Great Lakes ◽  
Host Rock ◽  
Volcanic Belt ◽  
Massive Sulfide ◽  
Sulfide Mineral ◽  
Water Levels ◽  
Great Lakes Region ◽  
Vms Deposits ◽  
Rock Alteration ◽  
Back Arc

The Paleoproterozoic (~1.8 Ga) Penokean Volcanic Belt (PVB) in the Great Lakes Region of North America hosts several polymetallic volcanogenic massive sulfide (VMS) deposits. These deposits were formed by back-arc extensional volcanism during the accretion of island-arc terranes along the southern margin of the Archean Superior Craton. This study reports δ34S values obtained from sulfide minerals collected from eight VMS deposits in the PVB: Back Forty, Bend, Eisenbrey, Flambeau, Horseshoe, Lynne, Reef, and Schoolhouse. The average δ34S values from most of these deposits lie within the mantle-range between −2 and 2‰, relative to Vienna Canyon Diablo Troilite (V-CDT). Average δ34S values from Back Forty and Lynne deposits are slightly higher, at 2.5 and 2.4‰, respectively. No systematic variation in δ34S was observed based on factors such as the kind of sulfide mineral, ore-texture, type of host rock, or the nature of host-rock alteration. The narrow observed range from the PVB offers a clear indication that sulfur in the mineralizing fluid, originated predominantly from a magmatic source. If there was a significant contribution of sulfur from seawater, the δ34S of seawater sulfur must also have been close to the mantle range. Slightly higher values from Back Forty and Lynne indicate minor involvement of oxidized sulfur at shallow water levels, possibly derived from the continental margin.

scholarly journals Evidence for voluminous bimodal pyroclastic volcanism during rifting of a Paleoproterozoic arc at Snow Lake, Manitoba

2017 ◽  
Vol 54 (6) ◽  
pp. 654-676 ◽  
Author(s):  
Kate E. Rubingh ◽  
Harold L. Gibson ◽  
Bruno Lafrance
Keyword(s):  
Massive Sulfide ◽  
Hydrothermal Activity ◽  
Stratigraphic Correlation ◽  
Pyroclastic Deposits ◽  
Volcanic Event ◽  
Vms Deposits ◽  
Flin Flon ◽  
Arc Setting ◽  
Gold Producer ◽  
Back Arc

The thrust-bounded McLeod Road – Birch Lake (MB) sequence occurs within the Paleoproterozoic Snow Lake arc (SLA) assemblage of the Flin Flon belt. Stratigraphic correlation of volcanic strata of the MB sequence with strata of the thrust-bounded Chisel sequence indicates that distinctive, submarine, eruption-fed, pyroclastic flow deposits are more extensive and voluminous than previously recognized (>10 km3). These voluminous felsic pyroclastic deposits define a distinct magmatic and explosive volcanic event during bimodal volcanism that accompanied rifting of the SLA. The felsic pyroclastic deposits define the remnants of a basin, or of nested basins, that formed during arc rifting and subsidence, and their eruption immediately preceded formation of the Chisel sequence volcanogenic massive sulfide (VMS) deposits. Although the Chisel sequence ore interval is recognized in the MB sequence, the lack of VMS-related alteration indicates that VMS hydrothermal activity was restricted to the Chisel portion of the basin. However, the MB sequence is host to the younger Snow Lake gold mine, a 1.4M oz (43 699 kg) gold producer. The overlying MORB-like Birch Lake basalts, if conformable with the MB sequence, may represent a progression from a rifted-arc to a back-arc setting. However, if they are thrust fault bounded, then they may represent the initial phases of arc-rifting, prior to the voluminous felsic pyroclastic eruptions. Correlation and integrity of stratigraphy between the thrust-bounded MB and SLA sequences indicates that the bounding thrust faults, which developed during accretionary processes, have less regional significance than previously interpreted.

Alteration and ore mineral characteristics of the Archean Coniagas massive sulfide deposit, Abitibi belt, Quebec

1998 ◽  
Vol 35 (6) ◽  
pp. 620-636 ◽  
Author(s):  
Pierre Doucet ◽  
Wulf Mueller ◽  
Francis Chartrand
Keyword(s):  
Hanging Wall ◽  
Massive Sulfide ◽  
Sulfide Mineral ◽  
Sulfide Deposit ◽  
Spreading Ridge ◽  
Massive Sulfide Deposit ◽  
Mineral Characteristics ◽  
Fe Content ◽  
Mineralized Zone ◽  
Back Arc

The Coniagas Mine in the northeastern Abitibi greenstone belt is a small, isolated Archean, volcanic-hosted, massive sulfide deposit rich in Zn-Pb-Ag. The Main lens, which is part of four massive sulfide lenses, is restricted to a 40 m thick massive felsic lapilli tuff unit of the 280 m thick sequence. The massive sulfides, a product of subsurface replacement, have features common to both Mattabi- and Noranda-type deposits. The Coniagas Mine sequence represents part of a small subaqueous volcanic edifice that probably evolved close to an arc or back-arc spreading ridge. A distinct alteration halo of chlorite + sericite ± epidote ± spessartine garnet in the immediate footwall and a hanging wall alteration assemblage of quartz + sericite ± epidote ± chlorite characterize the deposit. The sphalerite + pyrite + galena ± chalcopyrite sulfide mineral assemblage in the Main lens differs significantly from the pyrite + chalcopyrite + sphalerite + pyrrhotite ± galena assemblage in the stringer zone. Chlorite compositions are Fe rich close to the mineralized zone, with an Fe/(Fe + Mg) ratio of 0.38-0.48 in the hanging wall and 0.65-0.70 below the ore. Delicate sulfide textures including colloform pyrite and concentric sphalerite are consistent with a low temperature of formation, whereas higher temperatures are inferred for the stockwork zone. Electron probe microanalysis of sphalerite supports inferred hydrothermal fluid temperatures. The low Fe contents (6.7-10.8 mol% FeS) in sphalerite associated with colloform pyrite of the Main lens contrast with the elevated Fe content (12.7-14.1 mol% FeS) in sphalerite from the stockwork.

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