Naked Science Forum
Non Life Sciences => Geology, Palaeontology & Archaeology => Topic started by: OokieWonderslug on 12/01/2012 04:44:54
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I have been searching for a better geology forum for a while now and have had zero luck. It's like geology is a dead science or something. I am looking for a fast moving forum with knowledgeable geologists on it who are willing to give detailed answers to my questions. I go out and see formations and want to know about them, but have gotten very little feedback when I post.
Probably most of all I need to know why I haven't found any gold in my creek. It is a rift valley, with basalt dikes and sills at the floor of the valley. There is ample quartz in the creek and gold has been found within 10 miles of here. I find mudstone, tuff, and argillite in the creek bed along with the basalt and quartz. The source of most of the quartz appears to be from a vein about a quarter mile up the creek. It should have gold in it, shouldn't it? It appears the quartz vein formed from hot water coming off the basalt as it cooled, but it may have been at the surface at the time since the crystals in the basalt are slightly bigger than salt crystals. I don't know for sure since there apparently is no guide and geologists seem to disagree on everything. So what's the deal with my gold?
And actually, where is a forum that has detailed answers and maybe more than 10 posts a day to read? I need more than "gold is where you find it and there is no reason why it's not there."
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Hello OokieWonderslug,
Many of us are somewhat of generalists, not geologists.... So, while I find things like flat Granite Rocks interesting, my eyes tend to glaze over with very deep questions about the specifics on how they got there, especially when there is a lot of reference material already on the web.
Pictures are always worth 1000 words [O8)]
I see that there IS gold in South Carolina.
You said, "gold has been found within 10 miles of here."
Did you find it, or did you just hear that someone else found it?
I've done a little panning, only with marginal success in areas that I know to be "Gold Country", although some of the areas have been heavily dredged a century ago. I can remember panning with my Grandfather in a little inconspicuous creek where one could get a few flecks of gold, along with some good heavy Iron with every pan.
Anyway, if you aren't getting a lot of heavy black stuff in the bottom of the pan, then something is wrong.
About all I know is that gold is quite heavy, and it likes to collect around long-term obstructions, in very low spots in a creek or river. If you see gold on a beach, it probably isn't gold.
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Unfortunately, some of us are busy with other jobs and need to take extended breaks from the internet.
Most quartz veins do not contain detectable amounts of gold. Even though gold is rarely found without some sort of silica (quartz), the presence of quartz does not indicate the presence of gold. If gold wasn't so rare, it wouldn't be so valuable.
Unaltered basalt is not a good host rock for gold. It is probably not even a good source for gold, though the jury is still out on mafic sources for gold. Better are silicic igneous and volcanic terraines.
The limited work I did in North and South Carolina for gold exploration suggest the gold is older is far older than the Triassic rift systems.
As to why there isn't any placer gold- you still need some sort of source rock containing gold upstream. I assume the gold "found withing 10 miles of here" is not located upstream on your creek?
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The gold was found on Goose Creek in NC. They still find gold there, but tend to arrest anyone they find panning on the creek anymore.
I did not think the basalt was a possible source for the gold. I figured it to be the source of the heat that made water form the quartz vein. I can see the idea that the basalt heated water underground and it made the water pick up silica which was deposited in the vein. I was hoping it would pick up gold too and leave it in the quartz.
There is some black sand, but not much. The entire creek bed seems to be magnetic. I can drop a magnet into the creek and pull up loads of basalt and this red rock that is very attracted to a magnet yet is soft and when heated it explodes into shards.
The head of the creek is about a mile upstream. The two creeks are not connected in any way.
I would have thought the rifts were ideal places for gold. Shows how much I know I guess.
I am in the second rift valley going east from Charlotte. They continue pretty regularly to Albemarle.
About the basalt, what size should the crystals be for it to be a former lava? I want to know if the valley here was deeply buried when the magma came up or if it made it to the surface.
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Mafic volcanic rocks, like basalt, are low viscosity and flow fairly easily. Becuase of this, they don't tend to be good heat sinks. Silicic igneous rocks are high viscosity, which makes them much better heat sources.
As to crystal size- it depends. Some erupted basalts may have large crystals (phenocrysts) in a very fine grained groundmass. In others, there are few to no crystals. Phenocrysts usually form deep in the cooling magma chamber and are brought to the surface when the lava erupts.
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I think Bass has a good point.
Quartz is an indication that there COULD BE gold, not that there IS gold.
In the Northwest, I've seen veins of what appears to be quartz from a less than 1cm wide, to a few feet wide.
If you're getting the black sand, it sounds like you are at least coming close. I've normally seen quartz associated with granite, although I thought you could at least get small veins in a variety of rock types.
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I would expect black sand in areas with basalt. Basalts are iron rich and usually contain magnetite. Black sand (mostly magnetite) is commonly found in gold placers- not necessarily because it is associated with lode gold, but rather because it is one of the most common heavy minerals.