18.1. The mining exploration and development expenses referred to in subparagraph c or d of section 18 do not include any outlay or expense incurred to the extent that the outlay or expense constitutes an expenditure incurred by a person under an agreement entered into with an operator or another corporation or partnership, whereby the person incurs such expenditure solely as consideration for a share of the capital stock of the operator or of another corporation or partnership, for an interest in a partnership, or for an interest or right attaching to the share or interest.