Comment by jofer | Hacker News Reader

Comment by jofer | Hacker News Reader

Completely off topic, but as a geologist, phrases like this are a bit like nails on a chalkboard:

>> "Gold is still rare, but it's also everywhere, roughly speaking. It's geologically distributed like this because it leaves the center of the Earth through volcanoes and other cracks. The Earth's surface has cracks all over it, so gold is all over it."

In context, it's innocent enough, but it's the sort of thing that makes me twitch grumble... (The phrase "fault line" provokes the same reaction... It's not a line! Just say "fault".)

The main part is that a) gold isn't everywhere. It's concentrated in specific areas. and b) Why add the "center of the earth" part in? That's just silly... Next, most(ish) gold deposits are probably sourced from metamorphic fluids rather than igneous activity. It's true that there is a major category of gold deposits associated with felsic magmas, and another associated with oceanic crust production, but way off base that "gold comes from volcanoes".

Next:

>> "Coming from the center of the Earth is going to ensure that gold has qualities not usually seen on the surface."

What?? Yes, gold is relatively nonreactive and relatively soft. That's because it's a noble metal. It doesn't come from "the center of the earth"... Yes, the core is probably enriched in gold compared to the crust, but the gold we mine at the surface doesn't rise up from the core. (In fact, it was probably added by meteorite bombardment after the planet was formed.)

At any rate, enough ranting. Neither of these have any bearing on the topic of the article itself.

> Neither of these have any bearing on the topic of the article itself.

I disagree there. I think diligent fact-checking encourages readers' trust. While I don't expect the author to have consulted a geologist, when I read "It's geologically distributed like this because it leaves the center of the Earth through volcanoes and other cracks", I wonder if any of our lava/magma comes from the core, because most of our core is just iron and nickel. We can imagine what a volcano that spews iron and nickle would look like. A quick check on Wikipedia indicates that our magma is formed in the crust and mantle.

I tend to agree that the technical inaccuracies are glaring enough to detract from the article. And I'm not even a geologist - just an amateur rockhound who tends to pick up bits of gold along with the other (more interesting) things I find in the mountains and deserts of Utah.

I feel as though Dave Barry would jump in and point out that you've just shared an awesome band name:

Felsic Magmas

Cummingtonite.

(There is a long tradition, among earth scientists, of geological dirty puns.)

We do know how to make the bedrock.

My thing was crystallography. We do have the odd characteristic habit.

If you can show that ancient placer deposits were the result of meteor strikes and not volcanic activity I'll change the article. Everything I read pointed to volcanic activity.

If you mean modern mining activity, not germane.

Placer deposits are secondary in nature. I was referring to the original source of the gold, not later erosion and deposition.

Most major gold deposits are related to orogenic events (mountain building). A significant subset of these are related to fluids associated with felsic magmatism. However, the majority of orogenic gold deposits are linked to fluids that escaped during wide-spread regional metamorhpism, as opposed to volcanic activity. In other words, they're not related to igneous activity, but rather with burial and heating of large regions of rocks. (Note - Metamorphism is not melting.)

That aside, my main gripe is with using "center of the earth".

Yes, many gold deposits are linked to igneous activity. However, even if it is volcanic, what does that have to do with "the center of the earth"? Volcanoes don't source anything from that deep. Nothing comes from the core.

The metorite bombardment I was referring to is an early phase in Earth's history. After the core and mantle segregated, most of the heavy elements should have wound up in the core and been unable to escape. However, we see relatively high concentrations of many heavy elements in the crust and mantle. The leading hypothesis is that the heavy elements were added during the meteorite bombardment phase of the planet's formation. Because the core had already segregated, the heavy elements added this way were able to remain in the mantle and crust.

At any rate, sorry to go on a rather technical rant. It distracts from the main point of the article.

I've changed "center" to read "interior". I meant "center" as the complement of the surface.

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