Hydrothermal and Metamorphic Fluids of the Kidd Creek Volcanogenic Massive Sulfide Deposit

Abstract Primary fluid inclusions in what is thought to be syngenetic siderite preserve a record of the hy-drothermal evolution of the Kidd Creek volcanogenic massive sulfide deposit. The banded and zoned siderite is intergrown with sphalerite, chalcopyrite, and pyrite and occurs in irregular masses or in veinlike segregations. Microthermometric measurements suggest that the early, syngenetic carbonates in the ore zone crystallized from a predominantly aqueous fluid at a temperature of ca. 250° to 297°C and a mean salinity of 5.7 ± 0.5 wt percent NaCl equiv. Two distinct metamorphic fluids were identified at Kidd Creek, suggesting two distinct metamorphic events. First, albite porphyroblasts in the bornite zone, which contain numerous inclusions of xenotime and/or monazite, crystallized from aqueous fluids at about 450°C during peak metamorphic conditions. Their crystallization was probably contemporaneous with emplacement of the nearby Prosser porphyry, ca. 55 m.y. after ore deposition. Second, late subhorizontal quartz veins which crosscut the entire Kidd Creek deposit crystallized from fluids that had a similar composition and temperature to the fluids which crystallized the flat veins at gold deposits in the Timmins area. Fluid inclusion data indicate that some of the quartz veins at Kidd Creek formed at a temperature of 298° ± 31°C from CO2-rich fluids (with a minor CH4 component) having a salinity of 1.9 ± 1.1 wt percent NaCl equiv. The close similarities in fluid composition, temperature, and structural characteristics between flat veins and the subhorizontal quartz veins at Kidd Creek suggest that the emplacement of these veins represents a distinct event in the tectonic evolution of the Abitibi belt.