According to Mrs L Byron Rosehall LHG have been unable to substantiate these claims (other than a reference to manganese in area in 1st Stat Acc). Provided copies of corres with estate regarding this matter and evidence.
A Woodland History by Bell Ingram Forestry refers to "one of Lord Ashburton's first priorities (after acquiring the estate 1806) was to close a lead/manganese mine which operated in existing estate policies. The smelter & adj house were served by a canal dug by hand into the Kyle of Sutherland. Alongside was a spoilheap from the mining operations which was levelled when the mine closed & landscaped to create a small loch at the frontage of the garden - HAW 12/2003

Cottages see NC40SE0022
Canal see NC40SE0039

Gourlay, 21.4.1986: The remains of mine workings for the extraction of metallic minerals (probably zinc/manganese) lie immed to the SW of the house of Rosehall & now mainly blocked up. Another entrance reputedly emerged in the area now occupied by the pond. The drain from this pond also reputedly marks the position of a short canal, by which ores were transported to the kyle and thee by barge (to Tain?) The workings were constructed under the patronage of the landowner by imported Cornish miners. A row of cottages in Cornish Architectural style, survive nearby. Much orig documentation regarding these mining operations survive at the estate office - HAW 12/2003