Petrology and Geochemistry of Felsic Volcaniclastic Rocks along the Sherman Mine Road, Temagami Greenstone Belt, Strathy Township, Ontario

Abstract

<p>Felsic volcaniclastic rocks and intrusions along the Sherman Mine road, Temagami greenstone belt, were studied to determine if the petrological and chemical characteristics of these rocks indicate they are favourable hosts for volcanogenic massive sulphide deposits. Mapping of these felsic rocks was done at a scale of 1:5000 utilizing a 100 m spaced cut grid and pace and compass. Since outcrop is scarce and exposures are poor in this area, most correlation of the felsic horizons was done on the basis of trace and rare-earth element geochemistry.</p> <p>On the basis of the chemistry of the rocks, three distinct felsic horizons were defined. The quartz feldspar porphyries are FI type cacl-alkaline felsic intrusives with [La/Yb]n ratio from 16 to 29 and no Eu anomaly. The Link Lake and Sherman Gate horizons are FII type calc-alkaline volcaniclastic horizon with [La/Yb]n ratio from 5 to 7 and weak negative to positive Eu anomalies. The Upper and Lower Felsic horizons are FIIIa type tholeiitic rhyolite lava flows and valcaniclastics. These horizons have [La/Yb]n ratios from 1 to 3 and strong negative Eu anomalies from 0.16 to 0.42.</p> <p>Petrology and net transfer of material calculations indicate the Upper and Lower Felsic Horizons have been silicified, resulting in a net addition of Si and Al to these rocks. There is no distinct pattern of chemical changes which would indicate proximity to a single volcanogenic massive sulphide alteration pipe, however, an enrichment of the light rare-earth elements in the eastern section of the thesis area suggests this area maybe more proximal to an alteration pipe, and thus a vent. Lithological characteristics of the eastern section of the thesis area also suggests it is more proximal to a vent than the western section.</p> <p>Pyrite clasts are present in several of the volcaniclastic units. While the presence of sulphide rich clasts can be an indicator of proximity to a volcanogenic massive sulphide deposit, the textural and chemical characteristics of these clasts indicate they originated from shale horizons in this area. For this reason, these clasts should not be used as an indicator of proximity to a volcanogenic massive sulphide deposit.</p> <p>Trace and rare-earth element classifications indicate both the Link Lake and Sherman Gate horizons, and Upper and Lower Felsic horizons are favourable host rocks for volcanogenic massive sulphide style mineralization while the quartz feldspar porphyries, such as the Milne vent and the City Dump vent, are not. Although the felsic volcanic packages are relatively thin, potential exploration targets would be the upper contact of the Upper Felsic horizon and the Link Lake and Sherman Gate horizons./</p>