Lessees shall exercise diligence in the conduct of prospecting and mining operations, and on all leases referred to in § 214.8(a) shall expend annually in development work a sum which with the annual rental shall make an amount of not less than $5 per acre. On all leases referred to in § 214.8 (b) and (c) there shall be expended annually in development work a sum which inclusive of the annual rental shall make an amount of not less than $1 for each acre or fraction thereof included in the lease. The lands covered by each lease referred to in § 214.8 (d) shall be prospected for lead and zinc ores by drilling within 1 year test holes aggregating 2,000 feet unless a sufficient ore body is discovered to justify the sinking of a shaft to the ore body and the erecting of a mill when such tract may be released from further prospecting by the written consent of the superintendent: Provided, That within 90 days after an ore body of sufficient quantity is discovered, and shown by the logs or records of the drill holes, to justify the expenditure, the sinking of a shaft to the ore body, and the erection of a mill shall be commenced and continued to completion without cessation of work thereon, barring unavoidable accidents or causes beyond the control of the lessee.

Lessee shall keep upon the leased premises accurate records of the drilling, redrilling, or deepening of all holes showing the formations, and upon the completion of such holes, copies of such records shall be transmitted to the superintendent by the lessee after the first completion and of any further drilling thereafter, and a failure to so furnish report within the time prescribed shall be considered a violation of the regulations. Lessee shall, before commencing operations, file with the superintendent a plat and preliminary statement of how the openings are to be made and the property developed.