(a) Such association shall deposit with the Commissioner of Finance first mortgage securities to the amount of $25,000, approved by the Banking Board. Such deposit shall be held in trust by the Commissioner of Finance for the protection and indemnity of the residents of this territory with whom such association has or may transact business.
(b) All interest, premiums and dues which may accrue on the mortgages held by the Commissioner of Finance as provided in subsection (a) of this section may be collected and retained by the association depositing the same so long as such association remains solvent and faithfully performs all contracts with its members. When a mortgage is fully paid to such association, it may be surrendered to it, after such association has deposited with the Commissioner of Finance other first mortgage securities approved by the Banking Board, to the amount of those withdrawn.