Natural Resources

A High-Density Lake Sediment and Water Survey in Southeastern Labrador (NTS MAP AREAS 2M/13, 3D/4-5, 12-13, 12P/6-7, 9-11, 14-16, 13A/1, 9, 16, and 13H/1-11) )

J.W. McConnell and M.J. Ricketts

St. John's, Newfoundland, June, 2010

Abstract

A lake sediment and water survey was conducted in 2006 and 2007 over portions of NTS map areas 2M, 3D, 12P, 13A and 13H in southeast Labrador. The surveyed area is underlain primarily by rocks of the Grenville Province which, in this area, is subdivided into a northern exterior thrust belt and a southern interior magmatic belt. The Grenvillian thrust belt is composed predominantly of crust formed during the Labradorian Orogeny (ca. 1710 to 1620 Ma). The interior magmatic belt is characterized by numerous Grenvillian (ca. 1080 to 960 Ma) plutons emplaced into an assemblage of 1510 to 1450 Ma granitic intrusions that were themselves intruded into Labradorian crust.

Several instances of copper, nickel and molybdenum mineralization are known. One instance of thorium and uranium are reported and one of zirconium, possibly associated with rare earth mineralization.

A nominal sample density of one per four square kilometres was used, although the presence of some areas without suitable lakes reduced the effective sample density. Lake sediment samples were collected and analyzed from 2129 sites and water samples from 2234 sites. In a few cases a scarcity of material prevented analysis of the full analytical suite. In addition, one site in twenty was sampled in duplicate for quality control purposes. Sampling was conducted by float-equipped helicopter using a weighted tubular steel gravity sampler for sediment collection. Sediment samples were analyzed for a standard suite of 48 elements and loss-on-ignition. Additionally, 13 of the elements were analyzed using two different methods. Waters were analyzed for pH, conductivity and 27 elements.

The report provides summary statistics of the geochemical data, correlation analyses of selected sediment and water data, histograms, cumulative frequency plots, sample location maps and symbol maps showing the distribution of most elements and variables in sediment and water. The symbols are overlain on maps showing geology derived from 1:1 000 000-scale mapping and 1:250 000-scale drainage. The sample location maps show more detailed 1:50 000-scale drainage features.

There are many areas demarcated by samples having anomalous contents of various ore elements. Several clusters of samples with elevated contents of copper, nickel and zinc are found in the survey. Many of the clusters are over rock units that are elsewhere known to be mineralized in these elements. Although no uranium mineralization is recorded in the MODS database, several sediment and water samples with high uranium contents are present. Most of these are over granites or granitic rocks. Several areas in the southern part of the survey, mostly granitic terrane, are distinguished by samples with high levels of rare-earth-elements. These elements include, but are not limited to, dysprosium, lanthanum, terbium, yttrium and ytterbium. Some lake sediments collected over these granites are also enriched in niobium and tantalum. Also of possible follow-up interest are anomalies in titanium and gold.

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