Natural Resources

Open File LAB/1616 - A High-Density Lake-Sediment and Water Survey in the Fraser Lake Region, Western Labrador (NTS Map Areas 13L/05, 06 12, 13, 23I/08 and 09)

S.D. Amor

St. John's, Newfoundland, May, 2013

Abstract

A detailed, helicopter-supported lake-sediment and water survey was conducted over approximately 3300 km2 of the Fraser Lake region of western Labrador, on NTS map areas 13L/05, 13L/06, 13L/12, 13L/13, 23I/08 and 23I/09, northeast of the Smallwood Reservoir.

The sampled area is underlain by rocks of the Southeast Churchill Province (SECP). The dominant rock type, an early Mesoproterozoic mafic intrusive complex (the Michikamau Intrusion) that underlies the central portion of study area, has been the focus of exploration for magmatic Ni-Cu-Co mineralization. In addition, late Paleoproterozoic and early Mesoproterozoic gabbro-syenite and granite-charnockite-monzonite complexes in the region show indications of enrichment in rare-earth and rare-metal elements. The remaining rocks comprise Archean and/or Paleoproterozoic granite, tonalite and gneiss, and arkose and quartzite of the mid-Mesoproterozoic Seal Lake Group.

A total of 769 sites were sampled. The presence of larger lakes, notably the Smallwood Reservoir, reduced the nominal sampling density of one sample per 4 km2 to one sample per 4.3 km2. Water and sediment samples were collected at 679 sites, and water samples only at 90 sites. Field duplicate samples were collected at one site in 20.

Analysis of the sediment samples was carried out for 27 elements by Instrumental Neutron-Activation Analysis (INAA), for 31 elements by Induction Coupled Plasma Emission Spectroscopy (ICP-ES), for Ag by Atomic-Absorption Spectroscopy (AAS) and Loss-on-Ignition (LOI) by gravimetry. The water samples were analyzed for 24 elements by ICP-ES, U by ICP-mass spectrometry, fluoride ion by ion-specific electrode, conductivity by Corning conductivity sensor, and pH by Corning combination pH electrode.

The most conspicuous geochemical features include a large REE anomaly within the mapped bounds of the Michikamau Intrusion (23I/08 and 23I/09); a smaller REE anomaly, associated with Mo and some rare metals, over granitic gneiss, near the contact with an alkaline intrusive at the Québec border on 23I/09; a multielement (including REE) anomaly associated with the Proof Lake Complex on 13L/06; a zone of waters of high pH and conductivity, and low Al, that parallels the northwest shore of Sail Lake and is underlain by Neoarchean metatonalite and tonalite gneiss on 13L/05; and a strong lake water response in Cr and V over the Michikamau Intrusion on 23I/08. The presence of clastic material in sediment samples may give rise to false anomalies in a number of potentially economic elements.

The response to known Ni-Cu-Co occurrences in the Michikamau Intrusion, while not entirely absent, is indistinguishable from numerous others elsewhere in the surveyed area.

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