The Quemont Mine comprises massive stratiform Cu-Zn bodies in Archean volcanics (3.3 to 3.1 b.y.) of the Noranda-Matagami greenstone belt. The deposit appears to be volcanogenic and has a complex geological history. At least three modifying events are recognizable, including low-grade regional metamorphism and silicic dike intrusion during the Kenoran orogeny (2.5 b.y.), intrusion by diabase dikes 1.7 to 1.2(?) b.y. ago, and postdike remobilization of sulfides.Application of sphalerite geobarometry to the ores is problematic because of the low regional metamorphic temperature inferred from sulfur isotope geothermometry. Accordingly, indicated pressures of 6 or 8 kb appear to be too high for a suggested isotopic temperature around 300 degrees C. Isotopic temperatures of 300 degrees to >500 degrees are indicated for ores metamorphosed by later dikes. In general, these values show reasonable agreement with equilibrium conditions expected for low temperature greenschist metamorphism and subsequent contact metamorphism by diabase and felsic dikes. Sulfur isotope values for the deposit appear compatible with a volcanic-exhalative origin 3 b.y. ago.This study demonstrates that phase equilibrium was achieved by the Zn-Fe-S system at a uniform pressure corresponding to low-grade regional metamorphism, and that the corresponding equilibrium FeS content of spahlerite was preserved in ores that underwent subsequent contact metamorphism and accompanying recrystallization. On the other hand, sulfur isotope partitioning between coexisting sulfides responded to contact metamorphism by the dikes and approximately reflects the temperatures expected. Remobilization of sulfides by plastic flow may be responsible for some apparently anomalous isotopic results.
Cold springs emerging a long the contact between Devonian limestone and shale units in the northwestern Canadian Cordillera are presently depositing a radium-enriched barite sinter. A geological cross section through the springs area shows that groundwaters could circulate through a mainly limestone aquifer to depths of approximately 2 km. Some shales and volcanic rocks associated with the aquifer contain: barium, bound in feldspars; barite, pyrite, and organic matter hosted in shale; and radium in feldspars or produced by the radioactive decay of uranium associated with organic matter hosted in shale. Spring waters are of the [Formula: see text] type characteristic of water that has equilibrated with clay minerals. A subsurface equilibration temperature of 34 °C was determined by silica geothermometry, and 31 °C by magnesium-corrected Na + –K + –Ca 2+ geothermometry. Emerging waters are partly mixed with surface runoff and therefore these temperatures represent only minimum values. Assuming a normal geothermal gradient these temperatures indicate minimum groundwater percolation depths of 1 km. The δ 34 S values of barite sinter samples and one sample of aqueous sulphide range from + 15 to + 23‰, indicating a marine sedimentary rock source for sulphur. The corresponding δ 18 O values are negative, implying that the bulk of the sulphate oxygen is derived from groundwater during sulphide oxidation. These data suggest that the springs are fed by groundwaters that have percolated to depths of as much as 2 km, passing through an aquifer of Paleozoic marine sedimentary rocks and volcanic rocks. At depth these waters were reducing and probably weakly acidic. They dissolved barium, sulphur, and radium, which were transported to the surface where the water quickly oxidized and precipitated Ba(Ra)SO 4 .
