Lithophile elements and exploration using centre-lake bottom sediments from the East Kemptville area, Southern Nova Scotia, Canada

Abstract

The East Kemptville Sn deposit in southwestern Nova Scotia was discovered in 1978 by Shell Canada Resources, Limited using regional till exploration procedures. In 1977 and 1978, southern Nova Scotia was covered by a government-funded regional centre-lake bottom sediment survey (1 site per 5 km 2) for Cu-Pb-Zn-Ag-Ni-Co-Fe-Mn-Ca-Mg-Mo-Hg-As-U-LOI. Detailed lithogeochemical studies on drill core from East Kemptville have demonstrated significant roles for the elements Zn-Cu-Th-Li-F-Sn-Cl-Rb in the hydrothermal mineralization event. Most of these significant mineralizing elements were not analyzed as part of the original lake sediment survey. Later, in 1985, a subset of 55 lake sediment samples from the deposit area was analyzed for Sn, Rb, F and Cl. The pilot study was aimed to test the applicability of these lithophile elements to regional centre-lake bottom sediment geochemical programs. Anomalous values of F, Rb and Sn form a distinct halo of elevated levels southwest, southeast and northeast of the East Kemptville deposit, which appears to lie in an area of background values. The detailed till sampling undertaken by Shell Canada at East Kemptville provides a check, especially for Sn as to probable sources for these elements found in the centre-lake bottom sediments. Cassiterite is the main economic mineral at East Kemptville. Trace wolframite is found along with subsidiary chalcopyrite and sphalerite. Zn and Cu are recovered as by-products at the mine. Heavy minerals were separated from a bulk lake sediment sample from Moosefly Lake (the site of the highest Sn value from the regional survey subset). Spot analysis by scanning electron microscope indicates the presence of angular and discrete grains of cassiterite in the centre-lake bottom sediment, in addition to numerous grains of zircon, monazite and magnetite. The Sn anomaly in the centre-lake bottom sediment is due, at least in part, to the presence of discrete cassiterite grains. Their lack of abrasion would seem to indicate derivation from the nearby known cassiterite-rich tills. The lack of correlation of Sn data with organic material (as LOI) and the other elements probably indicates the dominance of mechanical over chemical dispersion processes in Sn distribution from the tills to the lakes. A common dispersion model for centre-bottom lake sediment surveys is one of initial glacial clastic dispersion, followed by subsequent hydromorphic dispersion into the lake basins. Although the dominance of hydromorphic processes is recognized, it is clear that clastic dispersion models must also be considered. Centre-lake bottom surveys appear to have greater application than previously presumed in the search for lithophile elements commonly dispersed as refractory grains.