I was reading in 2nd Nephi where Nephi ordained teachers and priests shortly after separating from Laman and Lemuel. Also when Jacob begins speaking he talks of being ordained after the Holy order of the Son of God (I know those are not the exact words). In the foot notes it then refers to the Melchizedek Priesthood. I assume the priest and teacher ordinations came from Levitical lineage (is this correct?) but where does the authority to confer the Melchizedek come from?
This is from Doctrines of Salvation, p.86, By Joseph Fielding Smith.
“The Nephites did not officiate under the authority of the Aaronic Priesthood. They were not descendants of Aaron, and there were no Levites among them. There is no evidence in the Book of Mormon that they held the Aaronic Priesthood until after the ministry of the resurrected Lord among them, but the Book of Mormon tells us definitely, in many places, that the priesthood which they held and under which they officiated was the Priesthood after the holy order, the order of the Son of God. This higher priesthood can officiate in every ordinance of the gospel, and Jacob and Joseph, for instance, were consecrated priests and teachers after this order.”
Lehi was a prophet of God, and brought the Melchizedek priesthood with him from the Old World.