In my paper “The Book of Mormon as Literary Alchemy: Joseph’s Magnum Opus and the Philosopher’s Stone,” I suggested that the “gold plates” that Joseph Smith had in his possession were not actually made of gold, and did not actually contain ancient historical records like Mormons traditionally think. But that doesn’t mean that there were not “gold plates” which were a kind of “hidden treasure” that Joseph really did discover within himself, which was the source of real divine wisdom, “ancient wisdom,” and which he taught could be found within all people as well. Such teachings can be found in other spiritual traditions too, including Buddhism. First I’ll review a few of Joseph’s writings about this “hidden treasure,” and then I’ll turn to the Buddhist concepts that seem to reflect a similar nature.

Joseph’s “Hidden Treasure”

Clearly, Joseph’s activities in his youth as a treasure digger really did happen. He really was involved in searching for buried treasure around his community, often using a seer stone as a kind of meditative object to try to pinpoint the location of this treasure through divination. It is my view that through extensive use of these folk magic exercises, which were also contemplative mystical practices that focused his consciousness, that Joseph actually did find buried treasure, but it was not the physical kind that pirates bury and uncover. It was an inner treasure, found deeply within human consciousness, which is usually hidden from human consciousness. Joseph may have not been fully aware of the nature of this treasure, and so he often conflated his inner discoveries in his consciousness with outer discoveries that he thought he had made, could make, or could perhaps alchemically transmute.
I proposed in my paper that the true “gold plates” were a visionary treasure that Joseph discovered within himself, deep within his consciousness and pure being that he taught could be found in all people, and it was from this deep source of Wisdom that Joseph “translated” the Book of Mormon text. This Wisdom is a perennial wisdom, sometimes called “ancient wisdom,” because it reappears throughout history and all around the world when mystics look deeply within themselves and discover the greatest and most precious of all truths—their own Divine Being, their Divine Nature, their Godliness, their Oneness with God, the Spirit, their Life, the Truth, Reality, the Absolute, the One, the True Self, the Eternal Self, the Christ, the Buddha-nature, the Atman, the Manifestation of God, al-Insān al-Kāmil (the “Perfect Human Being”), etc. There are many names for this found in nearly every spiritual or religious tradition.
Joseph referred to this “hidden treasure” several times in various contexts. In 1829, a year before the publication of the Book of Mormon, Joseph’s uncle, Jesse Smith, wrote a letter which referred to one Joseph wrote a year earlier:

“…[Joseph] writes that the angel of the Lord has revealed to him the hidden treasures of wisdom & knowledge, even divine revelation, which has lain in the bowels of the earth for thousands of years [and] is at last made known to him…”
(“Letterbook 2,” p. 59, The Joseph Smith Papers, accessed July 30, 2018, http://www.josephsmithpapers.org/paper-summary/letterbook-2/64. Emphasis added.)

At this early time Joseph seems to have thought that this “hidden treasure” was actually found in the ground, in the actual Earth, which could be dug up and translated. But I think what he actually found was that this wisdom was buried within himself, within his consciousness, within “Adam” (or Adamah, the Hebrew term for “ground” or “earth”). The treasure wasn’t found “out there” somewhere in the dirt, but within the “ground” of his being, as “Adam,” and this can be similarly found in the same “ground” of all beings.
It seems that Joseph himself came around somewhat to this interpretation as well a few years later. In 1833, three years after the publication of the Book of Mormon, Joseph recorded the revelation known as the “Word of Wisdom” (D&C 89). In it he said that by following this health code people would be blessed:

“…[they] shall receive health in their navel and marrow to their bones; And shall find wisdom and great treasures of knowledge, even hidden treasures; And shall run and not be weary, and shall walk and not faint.” (D&C 89:18-20)

It does not seem that following a health code would lead one to discovering more “gold plates” in the ground somewhere, but rather could lead to discoveries in a pure mind, in the spirit, in human consciousness, specifically “hidden treasures” of “knowledge” and “wisdom.”
The “hidden treasures” are noted again in a history of the church recorded between 1834 and 1836. In the handwriting of Warren Parrish, the circumstances surrounding Joseph’s recovery of the “plates” is described. He had trouble getting the “plates,” and he tries to figure out why:

“On attempting to take possession of the records a shock was produced upon his system, by an invisible power, which deprived him in a measure, of his natural strength. He desisted for an instant, and then made another attempt, but was more sensibly shocked than before. What was the occasion of this he knew not—there was the pure unsulied record, as had been described—he had heard of the power, of enchantment, and a thousand like stories, which held the hidden treasures of the earth, and suposed that physical exertion and personal strength was only necessary to enable him to yet obtain the object of his wish. He therefore made the third attempt with an increased exertion, when his strength failed him more than at either of the former times, and without premeditation he exclaimed, ‘why can I not obtained this book?’ [‘]because you have not kept the commandments of the Lord’, answered a voice, within a seeming short distance.”
(“History, 1834–1836,” p. 94, The Joseph Smith Papers, accessed July 30, 2018, http://www.josephsmithpapers.org/paper-summary/history-1834-1836/98. Emphasis added.)

Joseph had been schooled in all kinds of mythologies, mystical stories, and allegories about “hidden treasure” that could be discovered, but thought that this could be obtained through outward “physical exertion and personal strength.” He came to find that it was through inner spiritual humility and inner purity of mind that these “treasures” were revealed. The history then says that Joseph realized that it was only when “his heart was fervently engaged in prayer to the Lord, when his spirit was contrite,” that these visionary treasures were made known to him. In other words, it was when he was practicing deep prayer that his mind was opened to them. The visionary angel tells him, “if ever these sacred things are obtained they must be by prayer and faithfulness in obeying the Lord.” “No man can obtain them if his heart is impure, because the<​y​> contain that which is sacred…”
In the Book of Mormon text itself it notes that “treasures” that are “hidden up” will only be found again, or “redeemed,” by the “righteous.”

And it shall come to pass, saith the Lord of Hosts, yea, our great and true God, that whoso shall hide up treasures in the earth shall find them again no more, because of the great curse of the land, save he be a righteous man and shall hide it up unto the Lord.

For I will, saith the Lord, that they shall hide up their treasures unto me; and cursed be they who hide not up their treasures unto me; for none hideth up their treasures unto me save it be the righteous; and he that hideth not up his treasures unto me, cursed is he, and also the treasure, and none shall redeem it because of the curse of the land.

And the day shall come that they shall hide up their treasures, because they have set their hearts upon riches; and because they have set their hearts upon their riches, and will hide up their treasures when they shall flee before their enemies; because they will not hide them up unto me, cursed be they and also their treasures; and in that day shall they be smitten, saith the Lord. (Helaman 13:18-20)

I think this passage is best read metaphorically, not literally. It’s not talking about hiding gold and silver, but the treasures hidden within one’s inner mind and heart, the deepest treasures of our own divine nature. It is for this reason that it takes one who is “righteous” to uncover them, one who has their inner “heart set upon” God. This is echoed in other similar scriptures:

Lay not up for yourselves treasures upon earth, where moth and rust doth corrupt, and thieves break through and steal;

But lay up for yourselves treasures in heaven, where neither moth nor rust doth corrupt, and where thieves do not break through nor steal.

For where your treasure is, there will your heart be also. (3 Nephi 13:19-21; Matthew 6)

In a very real sense, the highest treasure is where your heart is. It is inside, in the heart of humanity and consciousness itself, something which no other person can touch or corrupt.

And now my sons, behold I have somewhat more to desire of you, which desire is, that ye may not do these things that ye may boast, but that ye may do these things to lay up for yourselves a treasure in heaven, yea, which is eternal, and which fadeth not away; yea, that ye may have that precious gift of eternal life, which we have reason to suppose hath been given to our fathers. (Helaman 5:8)

Again, this “treasure” is equated with heaven, that which is eternal, even eternal life, and is a “precious gift” (like gold), that we may become aware of and given. This is found within us, within the heart, within consciousness. I think this is what Joseph Smith became intimately aware of. In a revelation in 1829 he recorded:

Seek not for riches but for wisdom, and behold, the mysteries of God shall be unfolded unto you, and then shall you be made rich. Behold, he that hath eternal life is rich. (D&C 6:7)

It was the “mysteries of God,” this divine “wisdom,” this “eternal life,” that Joseph had found within himself, in deep prayerful states of consciousness, in unitive states of consciousness with God (Joseph spoke in the first-person as God during these revelations), that was the true “riches” or treasures of life.

Buddhist “Hidden Treasure”

As I shared in my paper, there is a tradition within Tibetan and Vajrayana Buddhism which closely parallels Joseph’s pursuit of a “hidden treasure” which turns out to be much more spiritual, mindful, and consciousness-oriented than objective physical treasure. It is the tradition of terma texts, which were known as “hidden treasure,” and these were discovered by spiritual adepts known as tertöns, also known as “treasure revealers.” The tradition was that ancient adepts had hidden these treasured wisdom texts in various places, and that later adepts would be led to them and discover them anew and translate them. But, as I noted in the paper, it’s unlikely that anything was actually hidden away in buried locations and later recovered, but rather it is thought that the texts were transmitted from mind to mind, or within pure consciousness itself:

In this tradition it is recognized that these terma texts were not literally hidden away in the ground, but were “concealed in the mind of the guru,” or in other words, “the true place of concealment is in the tertön’s nature or essence of mind.” These spiritual texts were metaphorically “buried” in the mind and nature of the adept themself, and recovered through attaining a purity of mind, a state of unitive consciousness. I suggest that this may have also been true of Joseph Smith, that he uncovered “ancient wisdom,” or perennial wisdom, which was concealed within his own mind, even within human nature.

The discovery of “hidden treasure” was really the rediscovery of forgotten teachings, hidden Wisdom, which was recovered from the depths of human consciousness itself. I’ve written more about the terma tradition here.
There are additional similarities elsewhere in Buddhism to this “hidden treasure.” There is a concept known as the Tathāgata, and the Gautama Buddha uses it to refer to himself, instead of the pronouns I, me, or myself. Traditional translations of the term are that it means “one who has thus gone,” or that is “beyond all transitory phenomena.” This inner nature of the Buddha is sometimes referred to as Buddha-nature, and certain sutras note that it refers to the inner eternal “Self” that is present in all beings, but often unknown to them, even as a “hidden treasury” waiting to be discovered:

“…[the Buddha] expounds the doctrine that this quality [of the hidden interior, wondrous treasury] is not only common to buddhas but to all living beings as well.”
(Blum, Mark L. (2013), The Nirvana Sutra, Vol. 1, BDK America, p. xv-xx.)

This “hidden treasury” is found in all sentient beings, but it is obscured to their vision by greed, anger, and other negative mental states of consciousness. Elsewhere it is likewise noted:

An unknown treasure exists under the home of a poor person that must be uncovered through removing obstructive dirt, yielding the treasure that always was there. Just as the treasure already exists and thus requires no further fashioning, so the matrix-of-one-gone-thus [i.e. the tathāgatagarbha], endowed with ultimate buddha qualities, already dwells within each sentient being and needs only to be freed from defilements.
(Hopkins, Jeffrey (2006). Mountain Doctrine: Tibet’s Fundamental Treatise on Other-Emptiness and the Buddha-Matrix. New York: Snow Lion Publications, p. 9)

In the Tathāgatagarbha Sūtra, it is noted that “The Buddha reveals how inside each person’s being there exists a great Buddhic ‘treasure that is eternal and unchanging’. This is no less than the indwelling Buddha himself.”
This inner “hidden treasure” of the Buddha is described as shining like “pure gold” in its preciousness within each person, and in one simile as “a golden figure within a burned clay mold.” This is nicely symbolized by the story of the Golden Buddha statue (see the photo at the top of this post). The story is retold in this short YouTube video:

Conclusion

There are many traditions around the world of a “hidden treasure” within, an alchemical Philosopher’s Stone, a golden Buddha-nature, “gold plates” of divine Wisdom, that all seem to be pointing towards our deepest eternal divine nature, that omega point within, the virgin point (le point vierge), the Christ, the Tao, the Atman that is one with Brahman. And this can only be discovered and known through deep spiritual exercises such as prayer and meditation, means that change our consciousness, through inner purity of mind, through throwing off all the “defilements” of the egoic “natural man” such as greed, anger, and hatred. When the mind is pure and clear, then the revelation of our true nature is made known, and our oneness with the Eternal is known directly.
As it’s written elsewhere, “The [Buddha-nature] is the ultimate, pure, ungraspable, inconceivable, irreducible, unassailable, boundless, true and deathless quintessence of the Buddha’s emancipatory reality, the very core of his sublime nature.” The same could be said of Christ, of the Tao, of Brahman, of Allah, etc. This can only be known through direct first-hand experience, as Thomas Clearly notes from a sutra, “Confused thinkers without guidance are in a cave of consciousness running hither and thither seeking to explain the self. The pure self has to be realized first hand; that is the matrix of realization… inaccessible to speculative thinkers.”