Liberation studies on tin-bearing sands off north Cornwall, U.K.

Abstract

This is a follow-up to a marine sediment geochemical exploration survey for tin placers off the N coast of Cornwall. Seven samples from the St. Agnes Head/Portreath area were selected from the traverse containing most of the geochemical anomalies for the assessment of Sn liberation characteristics. Heavy liquid separations were carried out on the shell-free fraction of the samples. It was found that above sp. gr. 4.3, Sn is present mainly in the form of monomineralic cassiterite grains and could be considered as liberated and recoverable. In the sp. gr. 3.32-4.3 fraction, tin is locked to a greater degree but could still be partly recoverable. However, in mineral fractions <sp. gr. 3.32, the bulk of the tin is severely locked in other minerals and is unlikely to be recovered economically. The high proportion of irrecoverable tin in the samples agreed with a mining contamination origin for the deposits. In placers formed under natural circumstances, monomineralic grains of cassiterite are more abundant than locked tin grains (Author's abstract)-R.A.H.