Natural Resources

Open File LAB/1620 - Kimberlite-Indicator Mineral Analysis of Esker Samples, Western Labrador

D. Brushett and S. Amor

St. John's, Newfoundland, July, 2013

Abstract

The discovery of economic concentrations of diamonds in kimberlites of the Superior Province, in Québec and Ontario, prompted the Geological Survey of Newfoundland and Labrador to conduct a reconnaissance, regional-scale field program in western Labrador in 2012. The survey area encompassed four 1: 250 000 NTS map areas (23G, 23H, 23I and 23J).

Examination of heavy mineral concentrations from 154 samples of esker sand and gravel collected over rocks of the Archean Ashuanipi Complex (Superior Province) and the Proterozoic Labrador Trough (Kaniapiskau Supergroup) and Grenville Province from Western Labrador have not revealed indications of the presence of kimberlites. There is evidence of the presence of other types of mineralization; these indications include:

  • Sedimentary or volcanosedimentary barite mineralization, possibly accompanied by base-metal sulphides, in mid-Paleoproterozoic metasediments of the Sims Group, Labrador Trough, centred in NTS map area 23G/16.
  • Magmatic Ni–Cu mineralization, possibly rather minor, in rocks of the Ashuanipi Complex in NTS map areas 23J/02 or 23J/03.
  • Minor pyritic Au–Cu mineralization, probably hosted in paragneiss of the Ashuanipi Complex, in NTS map area 23J/07.
  • ’Low-chromium’ (cumulus, as opposed to kimberlitic) diopside indicating magmatic Ni–Cu mineralization, in Grenvillian metamorphosed mafic intrusive rocks in NTS map areas 23G/01 and 23H/11.
  • Cu mineralization of unknown type in Labrador Trough supracrustal rocks in NTS map areas 23G/08 and 23G/09.
  • Magmatic Ni–Cu mineralization in gabbroic rocks of the Montagnais suite (Labrador Trough).
The composition of the eskers shows a close, although indirect, relationship with that of the underlying bedrock and it is concluded that the paucity of kimberlite indicator minerals is due to the absence of kimberlites in the eskers’ catchment area, and not because the sampling method failed to detect them.

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