Geoscience

Preliminary Exploration Database for Platinum Group Elements (PGE) in Manitoba

PGE Report Home
Introduction
Release Information
Viewing the Report
PGE Index Map
Analytical Data
Data Sources
Black Shales
References
Metal Prices
Rock Samples
Treatment of the Data
Acknowledgments


Black Shales

The initial black-shale geochemical database (Fedikow et. al., 1998) was developed for metallogenic and environmental/ epidemiological studies of Phanerozoic black shales in Manitoba. The metallogenic potential for black shales has been demonstrated worldwide as

  1. host rocks to precious- and base-metal mineralization,
     
  2. aquitards or ‘caprocks’ for focussing mineralizing fluids, and
     
  3. metal-enriched source rocks (Bloomstein and Clark, 1989; Colman et al., 1989).

Locally, their importance to mineral deposits has been demonstrated at Black Island in Lake Winnipeg (Fedikow et al., 1995), where the metal-enriched character of Ordovician black shales was interpreted to represent a link between mobilization of metals from a gold-enriched sulphide-facies iron-formation and the subsequent precipitation of these metals as variably coloured, metal-rich crusts on the shales. The chemical characteristics of these unique rocks will provide an opportunity to develop new metallogenic concepts relevant to mineral exploration in Phanerozoic sequences.

The project was designed to parallel and complement an environmental geochemistry study initiated by the Geological Survey of Canada (GSC) and described by Dunn (1990). The GSC study documents the chemistry of Cretaceous shales subcropping beneath glacial deposits, and seeks to address the apparent link between the high incidence of multiple sclerosis at Henribourg, Saskatchewan (Irvine et al., 1988, 1989) and the chemistry of soils and well waters. This association has been previously suggested by Gould and Warren (1980) and Hasanen et al. (1986).

The database has been established using a variety of analytical methods to generate a wide range of chemical elements, with the aim of providing baseline geochemical data to as wide a user group as possible. The geochemical data has been linked to Manitoba Phanerozoic stratigraphy, so that chemical characteristics of individual stratigraphic units can be determined and related to specific lithological units and associations.

Based on observations on the Nick property by Hulbert et. al. (1992), it was decided to include a select suite of black-shale samples, from the larger sample population described in Fedikow et. al. (1998), for PGE analysis. The basis for black-shale sample selection was the association of highly enriched elements, such as Mo, As, rare-earth elements, base metals and precious metals, in previously analyzed black shales. Table 4 includes all geochemical data for the select suite of black-shale samples from Fedikow et al. (1998), as well as the new PGE data contained in this report.

Black-shale samples identified as geochemically anomalous and included with this report represent a somewhat narrow range of units in the Phanerozoic stratigraphic time scale in Manitoba. The anomalous units include the Ordovician Winnipeg Formation, the Mississippian Bakken Formation and the Cretaceous Swan River, Morden Shale and Nibrara formations (Figure 2). New geochemical data for Au, Pt and Pd are included in this report and reported in Table 4. There is a narrow range of concentrations for each of these elements in the black shale samples selected for analysis.

Gold ranges from <1 to 86 ppb, Pt from <0.1 to 14.8 ppb and Pd from 0.5 to 13.3 ppb. The highest Au analysis (86 ppb) is from a sample of Cretaceous shale and the highest Pt and Pd contents are documented from two samples representing the Gammon Ferruginous and Pembina members of the Pierre Shale (First White Specks). These two samples contain 11.6 ppb Pt and 13.3 ppb Pd and 14.8 ppb Pt and 12.5 ppb Pd, respectively. The multi-element analyses of black shales will focus further studies of these unique lithologies as well as provide stimulus for the assessment of mineral potential.

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