The value established for metals and minerals on Earth is due to a handful of factors- primarily scarcity, transportation/ease of access, and uses.
Part of the reason I said the 'value' of gold is a meme is because . . . well, it is. Old world cultures were what placed value on gold, but it was ignored for some of the new world cultures simply b/c it lacked any use or in some cases scarcity. IIRC the Californian Indians could care less about the shiny rocks in the creeks but loved the steel tools. The scarcity of other things at times placed them at a higher value- when Iron started to be refined by the Hittites or glass was crafted from slagged sand. The processes were barely understood and getting any sort of usable material was very labor intensive. But it has had value, so it has perceived value going forward- sort of like bacon & eggs being a proper breakfast in the US. Or like the de Beers cartel making engagement synonymous with a diamond ring and creating a monopoly on diamonds that artificially keeps their value inflated (90% inflated?).
IIRC one of the sub-saharan African cultures/empires had salt as a currency because it could preserve food- which meant preserve the labor in creating food. They were not the only ones to trade for salt, but the most prominent as an example. Silk, spices, tea, alcohol, citrus, furs, oils, and many other natural products were all things that were traded at one point for the value but they had to be transported . . . the same with gold. FREX, during the California Gold Rush a dozen eggs cost (for inflation) over $90! Steak cost even more . . . during the various gold rushes, it was the people supplying food, tools, and other supplies that made the most because the scarcity of those items in part due to the influx of people outstripping the local infrastructure.
But you get out in space? Where the rubble of planets is floating around to pick over? Suddenly metals & minerals that might have been difficult to reach are on the 'surface' of floating rocks. Once you can mine floating rocks, it gets down to actual scarcity in content percentages and actual industrial uses. Titanium, Molybdenum, Tungsten, Magnesium, Rhenium, and other materials will be more accessible as well as being more 'pure' than can be found on a planet with a atmosphere. FREX, Molybdenum is not found naturally- I assume they are talking about on Earth b/c no one has prospected space yet- w/o oxidation so that it requires quite a bit of effort to separate from the compounds it is naturally found in.
Honestly, this is why BT has remote mining operations/settlements out in the periphery or on marginal worlds- moving ingots around in a gravity well is not cost prohibitive, and getting the power to run smelters is also easy. Thus pirates raiding mining sites makes sense, they can steal pure ingots and maybe find spare parts from among the MiningMechs on site along with explosives for home made rockets- win, win, win!
