Northwest Territories Geological Survey

The Tungsten belt, located along the Northwest Territories/Yukon border in the Mackenzie Mountains, represents one of the largest tungsten metallogenic regions in North America. Tungsten deposits along the belt are carbonate-replacement skarn deposits associated with peraluminous Cretaceous magmatism and are commonly spatially associated with gold showings. Of the known tungsten deposits, Cantung has the highest grade (reserve grades well above 0.7 WO3 %) and coarsest scheelite. However, other showings such as Mactung and Lened may be volumetricly larger or have been explored to a lesser extent. The relationship between intrusions and tungsten deposits is well established. Therefore exploration efforts have recently focused on identifying the "right plutons". Plutons of age and geochemical signature similar to those outcropping at Cantung have been widely recognized in the Tungsten belt but deposits have been more elusive. Comparable tungsten metallogenic provinces elsewhere in the world are characterized by the occurrence of regionally extensive crustal-derived batholiths that generate numerous deposits at spatial scales of hundreds of kilometers. Therefore, Cantung and Mactung may only represent a portion of the mineral endowment with additional resources yet to be discovered and characterized.

Both Cantung and Mactung are hosted in Cambrian sequences consisting of folded Precambrian to Silurian argillite and carbonate units. The ore occurs in the carbonates. The high buffering capability of carbonates makes them an unlikely candidate to generate long range geochemical anomalies. However, fluid-rock interaction in metapelites can cause trace element anomalies extending kilometers away from the main system. Regionally extensive Precambrian metapelites underlying and surrounding skarns in Cantung and Mactung provide a unique opportunity to test whether tungsten deposits generate distal geochemical signatures in the underlying and surrounding metapelites that could be used to identify additional non-exposed tungsten anomalies.
Skarns are characterized by the occurrence of alteration zonation with marked fronts. Geochemical changes in the different alteration zones provide information on how major and trace elements are buffered from proximal to distal in the mineralized lithologic unit. They also provide information on which elements are least likely to be buffered locally and therefore most likely to be good distal indicators. Therefore, local geochemical changes can provide a first order clue of potential distal indicators.

In this study we aim to define the local (decimeter scale) and regional (100s of meter scale) effects of fluid rock interaction in both the carbonate and the metapelites associated with well-known tungsten resources in the Tungsten belt. The objective is to define the characteristics and spatial scale of geochemical anomalies generated in the argillites below the skarn and within the carbonate by the mineralizing fluid and, additionally, by the spent fluid in the argillite above the skarn.