Mont. Code Ann. § 77-3-130

The department shall withhold from public inspection any information obtained from a mining lessee or permittee under this part if the information relates to proprietary geological information. The withholding is effective for as long as the department considers necessary, but in no event may be less than 5 years after expiration of the lease or permit, to protect the mining lessee's or permittee's economic interest in the proprietary geologic information against unwarranted injury or to protect the public's best interest.