The 1905 LDS edition accidentally omitted the repeated of in this conjunctive structure. The 1911 LDS edition continued this error, but the editors for the 1920 LDS edition restored the repeated of to the LDS text. This correction is consistent with virtually all other conjunctive phrases of the form “of gold and (of ) silver”. There are ten other instances with the repeated of in the text; in fact, one of the other instances occurs nearby:
But there is one example in the text without the repeated of for the expression “of gold and (of ) silver”:
Note that in this example the of is not repeated, neither before “their silver” nor before “all their precious things”. For each case of the expression “of gold and (of ) silver”, we follow the earliest textual sources with regard to the repetition of the preposition of. We should also note that there is an example without the repeated of in 2 Nephi 12:7, but there the order of gold and silver is reversed: “their land also is full of silver and gold”. This example is identical to the corresponding reading in the King James Bible (in Isaiah 2:7).
Summary: Maintain in Helaman 6:9 the repetition of the of in “of gold and of silver and of all manner of precious metals”, the normal Book of Mormon form.