Evidence for voluminous bimodal pyroclastic volcanism during rifting of a Paleoproterozoic arc at Snow Lake, Manitoba

Abstract

The thrust bounded McLeod Road -Birch Lake sequence (MB sequence) occurs within the Paleoproterozoic Snow Lake arc assemblage (SLA) of the Flin Flon Belt. Stratigraphic correlation of volcanic strata of the MB sequence with strata of the thrust bounded Chisel sequence, indicates that distinctive, submarine, eruption-fed, pyroclastic flow deposits are more extensive and voluminous than previously recognized (>10 km 3 ). These voluminous felsic pyroclastic deposits define a distinct magmatic and explosive volcanic event during bimodal volcanism that accompanied rifting of the Snow Lake arc. The felsic pyroclastic deposits define the remnants of a basin, or of nested basins, that formed during arc rifting and subsidence, and their eruption immediately preceded formation of the Chisel sequence volcanogenic massive sulfide (VMS) deposits. Although the Chisel sequence ore interval is recognized in the MB sequence, the lack of VMS-related alteration indicates that VMS hydrothermal activity was restricted to the Chisel portion of the basin. However, the MB sequence is host to the younger Snow Lake gold mine, a 1.4M oz. (43,699kg) gold producer.The overlying MORB-like Birch Lake Basalts, if conformable with the MB sequence, may represent a progression from a rifted-arc to a back-arc setting, however if thrust fault bounded they may represent the initial phases of arc-rifting, prior to the voluminous felsic pyroclastic eruptions. Correlation and integrity of stratigraphy between the thrust bounded MB and the SLA sequences indicates that the bounding thrust faults, which developed during accretionary processes, have less regional significance than previously interpreted.

Mechanical Analysis of Road Graben Slopes Based on Saturated-Unsaturated Seepage Theory

“…During the rainfall ingress process, rainfall penetration follows a specific trajectory of movement. In the case of specific geotechnical slopes, the unsaturated soil has a limited depth, where the saturated soil is located in the area below the unsaturated soil [14]. The process of rainfall infiltration from the appearance of the soil body to the interior of the soil body during rainfall is very complex.…”