Geometry of indicator mineral and till geochemistry dispersal fans from the Pine Point Mississippi Valley-type Pb-Zn district, Northwest Territories, Canada

Abstract

An indicator mineral and till geochemical dispersal case study was conducted at the Pine Point Mississippi Valley-type (MVT) Pb-Zn district in northern Canada to document glacial dispersal down ice from a known orebody. Indicator minerals in the non-ferromagnetic heavy mineral (specific gravity >3.2) concentrate of till down ice of the mined-out O-28 Pb-Zn deposit in the east end of the district include sphalerite, galena, and pyrite, as well as secondary Pb-Zn minerals anglesite (as coatings on galena), smithsonite, and cerussite. These minerals are sufficiently physically and chemically robust to survive glacial transport as well as post-glacial weathering in the carbonate-rich till of the region. Pathfinder elements in the <0.063 mm fraction of till, determined using a modified aqua regia digestion, include Zn, Pb, Cd, Tl, and S.Evidence for multiple ice flow phases, each with an erosional and depositional record across the district, includes cross-striated bedrock surfaces, streamlined landforms, and till clast fabrics. At the O-28 pit, two main phases of ice flow eroded and dispersed Pb- and Zn-rich debris first to the southwest and then to northwest, producing a fan-shaped palimpsest dispersal train defined best by indicator minerals, but also by till geochemistry. The last ice-flow phase during deglaciation had a minimal effect on the dispersal train geometry. This case study presents another example of complex glacial transport and dispersal by multiple ice flows that have been defined by both glacial ice flow indicators and glacial transport data. Complex ice flow and transport are to be expected over large parts of the glaciated terrain of Canada.The key implications of this study to mineral exploration are that: 1) till sampling is a viable exploration method in the district; 2) in the eastern part of the district where the till is generally thin (<5 m), surface till sampling will be cost effective; further west where till cover exceeds 30 m overburden drilling methods will be needed to collect till samples at depth; 3) indicator minerals and till geochemistry (transport data) combined with the reconstructed phases of ice flow define a palimpsest pattern of glacial transport in the region.