Mineralogy and geochemistry of an Archean tuffaceous exhalite: the Main Contact Tuff, Millenbach mine area, Noranda, Quebec

Abstract

The Main Contact Tuff, in the vicinity of Millenbach mine, Noranda, Quebec, is an extensive, although discontinuous, ore-related volcanic exhalative metalliferous sediment, or "tuffaceous exhalite," of Archean age. It was formed by the variable contribution of two constituents: (1) exhalite (chemical) composed mainly of pyrite, quartz, sphalerite, pyrrhotite, and chalcopyrite and (2) tuff (clastic) composed of quartz, chlorite, and sericite.Tuffaceous exhalites such as the Main Contact Tuff and the similar tetsusekiei of the Japanese Kuroko deposits (Miocene age) indicate a fossil hydrothermal system that may or may not have produced economic concentrations of metallic sulfides. The Main Contact Tuff displays cryptic variations, which provide exploration guides at different scales: (1) the Fe/[Fe + Mg] ratios of chlorite decrease from 0.63 to 0.32 over a distance of 0.3 km approaching ore from the north, and from 0.72 to 0.32 over 1.5 km from the south; (2) the FeO/[FeO + MgO] (sulfide-free) ratios of whole-rock specimens decrease from about 0.8 to 0.3 approaching the ore; (3) ilmenite is replaced in the ore zone by rutile and (or) sphene; and (4) the most manganiferous ilmenite is found close to ore. On the other hand, trace elements of exhalative origin (e.g., Ag, Co) in the Main Contact Tuff appear not to provide useful vectors towards ore. They are concentrated relative to normal pelagic rocks, but their distributions with respect to ore are complicated by multiple input sources and postexhalative redistributions of elements.

Depositional Gaps in Abitibi Greenstone Belt Stratigraphy: A Key to Exploration for Syngenetic Mineralization

“…Cherty exhalites such as the key tuffite (Kalogeropoulos and Scott, 1983; Fig. 9C) represent small-scale depositional gaps in the volcanic evolution of the Noranda Formation.…”

“…Hydrothermal circulation model: During a hiatus in volcanism, hydrothermal circulation produces chert breccia units crosscutting volcanic stratigraphy (Van Kranendonk, 2006), and meter-scale metalliferous stratiform cherts and/or iron formation proximal to VMS deposits (Kalogeropoulos and Scott, 1983;Van Kranendonk, 2006).…”

Geochemistry and morphology of metalliferous sediments and oxyhydroxides from the Endeavour segment, Juan de Fuca Ridge

“…Many ancient volcanogenic massive sulfide (VMS) deposits are overlain and flanked by ferruginous cherty sediments such as those in Kuroko deposits of Japan (Kalogeropoulos and Scott, 1983), the Noranda deposits of Quebec, Canada (Kalogeropoulos and Scott, 1989), and the Bathurst deposits in New Brunswick, Canada (Peter and Goodfellow, 1996;Peter et al, 2003). The rocks are thought to represent sediments that were deposited from hydrothermal fluids that vented at the seafloor and may be ancient analogues of the modern metalliferous sediments and oxyhydroxides in areas of volcanic activity.…”

Lithogeochemical and Mineralogical Methods For Base Metal and Gold Exploration

“…1. Base metal contents increase towards the ore zone, although rather irregularly (Kalogeropoulos and Scott, 1989).…”