The previous sentence is “And we did find all manner of ore, both of gold, and of silver, and of copper.” It is not a coincidence that discussing these specific metals led Nephi to a discussion of the “plates of ore” that he created and upon which he was writing.
It has long been known that plates of pure gold could not fit the description of the weight of the plates Joseph received. The best understanding of the composition of the plates is that they were an alloy known in the New World as tumbaga. It is an alloy composed of gold, silver, and copper. When combined in the proper amounts and washed with an acid, the alloy is golden. Geologist Jerry Grover commissioned some experiments to determine the percentages of each of the elements, and found that a plausible replica could be created that would hold the engravings, and even one which fit one of the descriptions that indicated that the letters were black on the golden background.
The weight of a set of tumbaga plates with the dimensions described for the plates delivered to Joseph are similar to the various estimates for them. No scales were used, so we only have the perceived weight as a guide.
As with other triggered asides, Nephi’s discussion of the physical makeup of the plates leads him to a discussion of the plates themselves, and the reasons for which they were created. Nephi made two sets of plates, and this verse discusses the first set, which we call the large plates of Nephi.
It is possible that some form of this verse was the intended end of the book of 1 Nephi. While it is the first verse of a chapter in our current edition, there was no division here in the 1830 edition. Everything that follows this verse can be interpreted as triggered asides that added unplanned information to the original concept for the book of 1 Nephi.
As a small note, the phrase “and it came to pass” is only found twice in this chapter. The first is here, where it is part of the historical narration. The reason is that most of this chapter contains asides that are not part of a narrative of events.