Red soil geology question

I grew up in the Gold Rush area and was told more than once that all gold across the western US probably originated in the same place, around Alaska, and was carried by successive glaciers down a stripe of the land mass - Alaska, Yukon, Dakotas, Colorado, Nevada, California. Supposedly you could tell where this material had been carried by the prevalence of red soil (which makes some sense, since gold oxide is a red pigment).

So here I am up in BoSox land, and I realize that the new-ish commercial and mall district is carved into low hills that are all bright brick-red soil and stone.

Any geologists with more than my modest education care to ramble?

:confused: Most red soil is red clay, mainly aluminum oxide. And one of the reasons gold is valuable and has been since time immemorial is that it’s usually found as the pure mineral and not as any oxides. My geology lessons are lost in the mists of time, but whomever linked red soil to gold seems to have had an overactive imagination. Given that they also seem to have confused “up” and “down” in a map with “up” and “down” in actual slopes, do they also believe that rivers always run north-to-south?

I recall getting the story from reliable sources (Rangers in the various Gold Rush parks, etc.) but I am asking here and now partly because I have no idea what the truth of the claim might be.

Glaciers most certainly did move from ca. Alaska to ca. Texas, so.

Gold oxide is the most common colorant in red glass - especially traffic light red lenses, IIRC. It’s been used since at least Venetian times to create “ruby glass,” and is used in precise amounts to render greenish glass colorless.

My understanding is that most red rocks and red soil are colored by iron oxides; basically rust. There may be some places where gold oxide causes red soil but it must be much less common than iron oxides.

–Mark

“Venetian times”, sigh… there is no such thing as “Venetian times”… do you mean medieval, Renaissance, since about the time the Murano glass works first got established, or what? And in any case, that’s not how gold is mined.

You obviously knew what I meant - the peak of the glassblowing art in Venice. Careful picking those nits lest you knock over something fragile. :slight_smile:

You seemed to be questioning the existence of Au[sub]2[/sub]O and its uses.

I’m not 100% sure of this, but I don’t think gold oxide occurs naturally in any significant amounts. It’s manufactured. Natural gold is mostly the pure metal, or sometimes in minerals combined with tellurium.

Isn’t gold that hasn’t washed into rivers still found in quartz deposits?

  1. Odd colored rocks was used by prospectors as clues to where to search for ores. Copper, silver, etc. Not sure about gold. And colors much more specific than “red” are involved.

There is no number 2.

The rest is 100% nonsense. Most gold is found in the Western US deep underground. They do hard rock mining to get to most of it. The rocks above them are many millions of years old. So we’re not talking about any of the Ice Ages we’re familiar with.

The easily found placer gold and such eroded out of these rocks. You find some good placer gold, work your way upstream and maybe you’ll luck out and find the mother lode. At that point you start digging and blasting.

Gold veins form in deep rock over millions of years (far longer than a glacier would last) due to pressure, heating and liquid water. Look at the origins of the ore in the Bingham Canyon Mine. Formed under pressure during the Cretaceous period. Millions of years of deep cooking formed a large copper deposit with gold, silver, lead, etc. thrown in.

Look at the terminal moraines from the most recent Ice Ages.

Gold appears in rock in minute overall quantities. To move enough rock to account for the gold would result in terminal moraines the size of mountain ranges. These mountains would be trivially distinguishable from the actual mountains in the west.

It doesn’t make sense that the west coast gold all originated in Alaska. Gold is usually found around volcanoes that have spewed a lot of quartz. Apparently there were a lot of those in Alaska, but no reason to think there weren’t any further south. There is gold around Nwingland, but not that much and most of the gold was probably washed out to sea eons ago. Diamond Hill up the road from me probably spewed a lot of gold that is buried beneath tons of mud in the bottom of Narragansett Bay or under hundreds of feet of glacial deposits. There are records of a couple of mines in colonial times but no evidence that they ever produced much. I think people still look for gold somewhere near the CT border. I heard about a hard rock mine in the Adirondacks that still produces small amounts, but never enough to get major commercial interest. OTOH gemstones can be found just about anyplace, IIRC there’s amethyst down around Coventry. Unfortunately the diamonds at Diamond hill are just white quartz.

[QUOTE=Amateur Barbarian]
I grew up in the Gold Rush area and was told more than once that all gold across the western US probably originated in the same place, around Alaska, and was carried by successive glaciers down a stripe of the land mass - Alaska, Yukon, Dakotas, Colorado, Nevada, California.
[/QUOTE]

Not true. The Mother Lode, the largest California deposit, was an *in-situ *quartz vein deposit, and others such as the Carlin deposits of Nevada, are hydrothermal in origin.

No, they didn’t.

In Anne of Green Gables, Anne wanted to know why the roads were red when she moved to Prince Edward Island. Later on in the book, she notes that she found out why in school. (However, the author doesn’t mention the reason.)

I certainly am. I have never heard of gold oxide. A quick internet search reinforces my ignorance. There is an oxide of gold: Au2O2. It apparently never occurs naturally and decomposes at 160degC. A bit more than a hot day, but hardly hot.

So, I can’t find any evidence that gold oxide exists in nature, much less in quantities large enough to be noticable in the soil.
And adding gold to molten glass as a colorant is not related at all to any oxides. Like most elemental colorants, I believe the gold atom simply displaces a spot in the glass matrix and changes the refractive properties of the glass.

Red colour in glass is not gold oxide. It is just gold. Very very small (nano) sized particles of gold. It is this small size that provides the optical properties. Ruby glass is arguably the first ever man-made nano-material.

Red sand here is Oz is iron based. A very large fraction of the surface of the country is red. It is anything from iron oxide surface staining to outcrops of high quality iron-ore.

Mineral deposits of gold come in two basic forms. Alluvial - where the gold has been washed out of the rocks over the aeons and concentrates in stream beds and sediments. Or it is gold in situ in the rocks - where it forms veins. That gold was transported there by ancient geological processes. The gold is actually dissolved in very hot water under extreme pressure and migrates up through faults and fissures in the rock toward the surface. Eventually it will be deposited out of solution. Another material that moves in the same way is silica, and when deposited as quartz leads to the common association of gold veins and nuggets in quartz.

Prospectors for any mineral will use clues about the presence of different geological processes to guide ideas about what else might have been happening. Something as simple as noticing that gold is associated with red sand in one area may be useful when a nearby area is similarly red, and maybe the same mineralisation processes were occurring. But as a general rule, there is little chance it is useful. There is just too much variation possible.

Yep, as veins of the pure metal. Gold nuggets are pebbles composed of gold rather than of the much more common (in pebbles) silica or carbonates.

It’s now thought that most of the gold in the Universe came from colliding Neutron stars.

Cool - so, we are still stardust, but a tiny part of us is neutron stardust.

If our universe is a simulation, this is like bitcoin mining. The aliens decided to make gold the currency of our universe; to make more they have to collide neutron stars, which is CPU-intensive.

Related to these points that there’s a lot more to mineralogy than just “red dirt”, I came across this picture and explanation today: http://epod.usra.edu/blog/2016/11/archive-acid-mine-drainage-chemistry.html

Here in the space of 50 feet we see two very different shades of “red” denoting two very different (but still iron-based) chemistries in action.

No gold involved in this example, but I thought it interesting and mostly relevant nonetheless.

Glaciers might have spread from Alaska to Texas, but they didn’t move there. Rather, the colder it gets, the further south glaciers will form. Any glaciers that were ever found in Texas formed in Texas, once it got cold enough for Texas to form glaciers.

Once again:No, they didn’t. Texas was never glaciated in the last ice age, not even close, and what is now Alaska didn’t even exist during the previous Ice Age.

California has some glaciation, as it still does,but the glaciers are and were alpine in origin, not from the great northern ice sheets.