POSSIBLE SOURCES OF UNUSUALLY HIGH BORON CONCENTRATIONS IN THE McIntyre GOLD MINE TAILINGS, TIMMINS, ONTARIO

Geochemical studies of boron in mesothermal gold deposits suggest that there is a correlation between gold mineralization and boron. Geochemical closure assessment of the ~100 year old tailings dam at McIntyre mine reported B concentrations in the bulk tailings, its leachate, and groundwater that exceed anticipated future environmental limits. B occurs as water insoluble and weathering resistant vein- or wall rock-hosted tourmaline in the Porcupine camp. In this study we seek to identify other sources and mechanisms to explain the high amount of soluble B in the tailings.

Preliminary crush-leach fluid inclusion analysis of quartz carbonate tourmaline veins from McIntyre, Davidson Tisdale, and Buffalo Ankerite mines indicate that the aqueous portion of the mineralizing fluid contains 40 to 350 ml/L B. The McIntyre mine #5 tailings dam was sampled using a hand auger at locations previously shown to have high B concentrations. Eight boreholes were sampled every three feet and continuous sampling was employed for two boreholes to document chemical changes with depth, in particular the transition from orange-brown, oxidized material to bluish-gray, unoxidized material. A layer of white, efflorescent minerals that precipitated on the side of the tailings dam coincides with the oxidized layer in nearby boreholes.

The tailings are fine sand to silt sized, separated by thin intervals of clay. Samples were dried, homogenized, and texture and color characterized, before splitting. Leachates where extracted using a shake-flask procedure (water to sample ratio of 3:1) and analyzed for soluble B by ion chromatography. Anhydrite and calcite, common vein minerals in the McIntyre mine, were also tested for B after dissolution in HCl. The crystals that precipitated on the tailings dam were separated and studied optically and with SEM, Raman Spectroscopy, and XRD. The EDS spectra indicate the presence of gypsum and a hexagonal/pseudohexagonal hydrous magnesium phase. The soluble B in the #5 tailings dam is most likely a result of gangue minerals breaking down and B-rich fluid inclusions. Another possible but less likely explanation of the B anomalies is borax used as a flux to refine the gold ore.