Sulfur isotope characteristics of metamorphosed Zn–Cu volcanogenic massive sulfides in the Areachap Group, Northern Cape Province, South Africa |
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Authors: | Russell Bailie Jens Gutzmer Harald Strauss Eva Stüeken Craig McClung |
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Institution: | 1. University of the Western Cape, Cape Town, South Africa 2. TU Bergakademie Freiberg, Freiberg, Germany 3. Westf?lische – Universit?t, Münster, Germany 4. University of Washington, Seattle, Washington, USA 5. University of Johannesburg, Johannesburg, South Africa
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Abstract: | Zn- and Cu-rich massive sulfide ores of volcanogenic origin volcanogenic massive sulfide (VMS) deposits] occur as stratiform/stratabound
lenses of variable size hosted by gneisses, amphibolites, and schists of the Areachap Group, in the Northern Cape Province
of South Africa. The Areachap Group represents the highly deformed and metamorphosed remnants of a Mesoproterozoic volcanic
arc that was accreted onto the western margin of the Kaapvaal Craton during the ∼1.0–1.2 Ga Namaquan Orogeny. Sulfur isotope
data (δ34S) are presented for 57 sulfide separates and one barite sample from five massive sulfide occurrences in the Areachap Group.
Although sulfides from each site have distinct sulfur isotope values, all δ34S values fall within a very limited range (3.0‰ to 8.5‰). Barite has a δ34S value of 18.5‰, very different from that of associated sulfides. At one of the studied sites (Kantienpan), a distinct increase
in δ34S of sulfides is observed from the massive sulfide lens into the disseminated sulfides associated with a distinct footwall
alteration zone. Sulfide–sulfide and sulfide–barite mineral pairs which recrystallized together during amphibolite- and lower
granulite facies metamorphism are not in isotopic equilibrium. Sulfur isotope characteristics of sulfides and sulfates of
the Zn–Cu ores in the Areachap Group are, however, very similar to base metal sulfide accumulations associated with modern
volcanic arcs and unsedimented mid-ocean ridges. It is thus concluded that profound recrystallization and textural reconstitution
associated with high-grade regional metamorphism of the massive sulfide ores of the Areachap Group did not result in extensive
sulfur isotopic homogenization. This is similar to observations in other metamorphosed VMS deposit districts and confirms
that massive sulfide ores remain effectively a closed system for sulfur isotopes for both sulfides and sulfates during metamorphism. |
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