Rheingold, et al.

A companion piece of sorts, to We use Every part of the Dragon.*

Rheingold

If you take the Rheingold and forge it into a suitable personal ornament, it will give you.....worldly power.

But you have to give up......Love.

And it is guarded by......Seductive beguiling maidens.

It was set there by a Demiurge who may well work against you -.......A maimed manipulator with a rune-carved sceptre.†

Alberich, from Die Nibelungen: Siegfried (1924, Fritz Lang).
See also here.

Nile Tin

If you take the Nile Tin and forge it into a suitable personal ornament, it will give you.....Power over depictions.

But you have to give up......Artistic Taste

And it is guarded by......Ibises with poisoned talons and sagacious arguments.

It was set there by a Demiurge -.......A feather-cowled cosmic charioteer.

Ganges Iron

It will give you.....power over conflicts, contests and contention.

But you have to give up......Regret.

And it is guarded by......Humanoid snakes who know all your shameful secrets.

It was set there by a Demiurge -.......A four-faced mother of many riding a crocodile.

Mississippi Lead

It will give you.....power over transactions.

But you have to give up......All hate, wrath and enmity.

And it is guarded by......Ghostly, loathsome, mocking horsemen.

It was set there by a Demiurge -.......A dark-suited cigar-smoking shady patrician.

Yangtze Silver

It will give you.....power over records and truth-telling.

But you have to give up......Sleep, forgetfulness and the ameliorative effects of time.

And it is guarded by......Giant, officious, bureaucratic carp.

It was set there by a Demiurge -.......A smiling, flower-wreathed immortal Princess.

"I have been in love with [RHINE] gold. I love its colour, its brilliance, its divine heaviness. I love the texture of [RHINE] gold, that soft sliminess that I have learnt to gauge so accurately by touch that I can estimate the fineness of a bar to within one carat. And I love the warm tang it exudes when I melt it down into a true [RHINE] golden syrup. But, above all, Mr Bond [SIEGFRIED], I love the power that [RHINE] gold alone gives to its owner – the magic of controlling energy, exacting labour, fulfilling one’s every wish and whim and, when need be, purchasing bodies, minds, even souls."

Mekong Copper

It will give you.....power over the 'terrestrial spiritual'. You cannot bar the doors of heaven or hell, but you can lead people into temptation or block chakras or make the worldly man into a saintly hermit.

But you have to give up......Trust.

And it is guarded by......Singing mummified monks.

It was set there by a Demiurge -.......Spiteful, demonic twins.

Volga Zinc

It will give you.....power over wildness: human passions, beasts and wilderness.

But you have to give up......Any sense of community or togetherness. You can become 'one flesh' with a partner, but cannot bond with anyone else.

And it is guarded by......Restless, boisterous warriors clad in pelts. 

It was set there by a Demiurge -.......A muscular temperamental thaumaturge who carries his ever-glowing furnace on his back.

Niger Platinum

It will give you.....power over 'Higher feeling' - elevated, refined sentiments or anything aspiring to the same.

But you have to give up......Any sense of novelty, invention or discovery. Nothing will ever be new to you.

And it is guarded by......Abusive lion-headed apes.

It was set there by a Demiurge -.......A Crone in elaborate robes and a tall headdress.

Cover of Tom Holt's Expecting Someone Taller - an introduction to Wagner parody for me.
Don't pay too much attention to the cover.

If you gain and try to alloy any of the above metals, every single listed Demiurge will appear and start hitting you with cricket bats until you stop. 

*Other inspiration from this review. I have moved away from the previously encountered scheme of the metals of the ancients - getting liquid mercury out of a river seems a troublesome business. So, I refer to this list, excluding the non-metals, as well as mercury and bismuth.

† So.....The origin of the Rhiengold is never entirely clear, either in the Volsungsaga or the Ring Cycle. I have elected to associated each metal with some distant creator - with their precise level of power kept fairly vague - hence demiurge rather than deity, &c. This is in keeping with one piece of inspirational media and also with the whole 'Gods brought low by their own tools/schemes' element of the Ring Cycle.