[defrost]

"Dense deposit" means there's a lot of gold per tonne of not gold.

Manual mining produces good rewards in nugget rich grounds with dense primary rewards, if you move (say) 10,000 tonnes of material you find a lot of gold, even without extra processing (such as gold cyanidation).

When you hit low grade regions there simply isn't as much gold present - not only do you still need to move 10,000 tonnes of material, you know also need to chemically bind and extract in order to get less gold overall.

The pattern is, the easy is cheap (in terms of effort), the harder stuff costs more (in terms of effort), and minor advances in technique aside .. everything ladders upwards to cost more in extraction effort for less return.

It's been true for gold, for copper, for fossil fuels, etc.

Historically you can see hard data for this in something like [1] which is sadly a subscription service.

[1] https://www.spglobal.com/marketintelligence/en/campaigns/met...

[eesmith]

> "Dense deposit" means there's a lot of gold per tonne of not gold.

I do understand that.

In 1880s South Africa (before cyanide was used), was that remaining ore considered a dense deposit? I don't know.

https://en.wikipedia.org/wiki/Gold_extraction#Industrial_era informs me "mining ... began to slow down ... as the new deposits being found tended to be pyritic ore. The gold was difficult to extract from such ores."

I interpret this as meaning that with the technology of the 1880s it was not considered a dense deposit, and earlier dense deposits were being exhausted.

This is tied back to your original statement "once dense deposits are exhausted extraction costs substantally increase even in the face of more sophisticated technology."

If it wasn't a dense deposit, then did the costs substantially increase with cyanidation? (Not total cost, but cost per unit production.)

[defrost]

> If it wasn't a dense deposit, then did the costs substantially increase with cyanidation? (Not total cost, but cost per unit production.)

I made a broad long term statement that's true over multiple decades and centuries - if you take a keyhole view there will be times when the long term trend is bucked.

I don't specifiaclly know the exact answer to your question (although it can be worked out by a research student with a month or two to spare) but I would hazard that profits from gold mining were dwindling with a high cost of getting some value from fines .. and then cyanidation made things profitable again.

It's a market with supply | demand and a finite amount of gold in the crust - nuggets are no longer laying aboutto be picked up, and now many tonnes of sand and grit need to be centifuged | screened | shaken to get a concentrate .. and as the profit from that dwindles and price/kilo rise due to limited supply - it become possible get more gold from the concentrate with a little additional cost (in time + chemical) and profits rise again.

Whatever specifically happened in a short time window in a specific location though; the long term trend remains, more effort for less return of product.

[eesmith]

I understand how you can think of it as a keyhole view.

Instead, I think it's that I want "dense deposit" to mean something fixed, so we can look at a Roman gold extraction operation and say "yes, that is a dense deposit" or at a South African mine and say "no, that is not a dense deposit" independent of the technology in use.

Here's a thought experiment for that research student - which would cost more using current wages:

- extract 1 ton of gold from a deposit as rich as (say) the Dolaucothi Gold Mines when it used by the Romans, and using only Roman techniques.

- extract 1 ton of gold from a deposit equivalent to a South African mine in 1900, using cyanidation techniques of that era.

(I don't know if 1 ton is too low or too high to be reasonable.)

> nuggets are no longer laying about to be picked up

This isn't entirely true. People do still fund nuggets by happenstance. A news search finds things like https://www.yahoo.com/entertainment/family-finds-24k-gold-nu... from a few years ago.

But yes, they aren't the types which kick of a new gold rush.

In any case, Roman gold extraction wasn't just from picking up nuggets either, so I'm not sure that's quite the right comparison.