Findings and interpretation from a new geochemical lake sediment survey in the Ungava Peninsula
Charles Maurice and Daniel Lamothe, MRN
On September 19, representatives from the Ministère des Ressources naturelles were at the 10th annual CONSOREM-DIVEX technology forum in Rouyn-Noranda to present findings and interpretation from a new geochemical lake sediment survey in the Ungava Peninsula. The following is a summary of their presentation.
Almost 3,000 lake sediment samples were collected from an area located north of the 61st parallel in the Ungava Orogen and the northern part of the Superior Province. The area had never been targeted by a lake sediment survey, and was one of the missing links needed for complete coverage of Québec’s Precambrian geological provinces. The samples were collected during the summer of 2011 using an average sample density of one sample per 13 km2, covering a total area of 39,000 km2. No samples were taken from protected areas or from a region of roughly 1,500 km2 northeast of the Povungnituk mountains, where very few lakes are found.
The sediments were analyzed for a series of 53 chemical elements using inductive coupled plasma mass spectrometry after 0.5 g of material was partially dissolved in aqua regia. The new data was published on SIGEOM in March 2012, and the PRO2012-03 report identified 14 zones of interest for mineral exploration. One such zone is located in the northern portion of the North Domain, near the Narsajuaq arc, and is characterized by lake sediments with high Cu, Ag, Au and Hg values. The identification of the zone led to the staking of 276 claims by the company Khalkos and the discovery of new Au, Ag and Cu indicators during the summer of 2012.
For the survey as a whole, 27 samples showed anomal Au content over 15 ppb, above the 99th centile. The samples were reanalyzed using pyroanalysis with a larger sample size (30 g). Nineteen samples returned results under 5 ppb, only five gave reproducible values of 15 to 20 ppb, and three did not contain enough material to complete the reanalysis. The results illustrate the problem of the amount of material needed per analysis to counteract the nugget effect. The situation is complex given the small quantities of materials harvested in certain lakes in northern regions.
Other chemical elements must be used to plan exploration campaigns targeting gold. Apart from the so-called “traditional” elements (such as As and Sb), several others, previously unusable or unavailable, are now offered in ICP-MS analysis groups and may help identify geological environments favourable to certain mineralization types. The association of high concentrations of Bi and Te in lakes close to known Archean auriferous indicators could, for example, point to the presence of auriferous mineralized systems containing bismuth tellurides.
The new geochemical data from lake sediments on the Ungava Peninsula will help improve our understanding of an area that has seen little exploration for substances other than Ni and Cu, and will assist in targeting the discovery of geological environments suitable for various types of mineralization.
The full presentation of the findings and interpretation from a new geochemical lake sediment survey in the Ungava Peninsula is available in PDF format (5.4 Mo) (in French only).