Sec. 641. Establishment and maintenance of program for exploration; financial assistance. 642. Exploration contracts. (a) Terms and conditions; interest rates. (b) Deposit of royalty payments. (c) Certification of exploration projects; payment of royalties; time limitation on payment; royalty agreements. (d) Production. (e) Rules and regulations; adjustment of contracts. (f) Availability of funds. 643. “Exploration” defined. 644. Advice and assistance by Government departments and agencies; expenditure of funds. 645. Repealed. 646. Authorization of appropriations.