Natural Resources

Open File 013A/0089 - A High-Density Lake-Sediment and Water Survey in the Alexis River Region, Southeastern Labrador (NTS Map Areas 13A/02, 13A/07, 13A/08, 13A/10, 13A/14 and 13A/16)

S. Amor

St. John's, Newfoundland, October, 2013

Abstract

A detailed, helicopter-supported, lake-sediment and water survey was conducted over approximately 5500 km2 of the Alexis River region of southeastern Labrador, within NTS map areas 13A/02, 13A/07, 13A/08, 13A/10, 13A/14 and 13A/15, west of Port Hope Simpson.

The sampled area is underlain by rocks of the Grenville Province. These are predominantly granitic in the south, and form a component of the Interior Magmatic Belt. To the north, the Exterior Thrust Belt consists of metamorphosed supracrustal rocks, predominantly sedimentary, as well as mafic and felsic-intermediate intrusive rocks. Search Minerals’ 2010 REE discoveries south of Port Hope Simpson lie partly within the area of coverage.

A total of 854 sites were sampled. The absence of lakes and ponds of any kind over much of the survey area reduced the nominal sampling density of one sample per 4 km2 to one sample per 6.4 km2. Water and sediment samples were collected at 833 sites, and water samples only at 21 sites. Field duplicate samples were collected at 1 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 Spectrometry (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 response to the known REE mineralization takes the form of a zoned anomaly, with different element signatures, in sediment and in water, over Search Minerals’ REE discoveries and to the southwest and northeast. Elsewhere, the most conspicuous geochemical features include several other areas of enrichment in REE and REE pathfinders, as well as of an element association in sediments that includes Al, Ba, Be, Ca, Cr, Cs, K, Mg, Na, Nb, Rb, Sc, Sr, Ta, Ti and Zr. This latter association is believed to be related to the amount of inorganic clastic material in the sample, but variations in the relative amounts of these elements, in the anomalies defined by the association, suggest variations in sediment provenance. An anomaly of Au and certain Au pathfinders is present in the southeast of the survey area, associated with metamorphosed felsic volcanic rocks. The probable effects of marine incursion can be seen in the Br content of the lake sediments, and the Na content of the waters, in lakes within about 20 km of the coast.

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