19

That is the multimillion dollar question! "looking for surface formations" is indeed one way, and it was the main method of exploration in the past. This does not necessarily mean that you directly see the ore deposit in front of your eyes. Many ore-forming systems are accompanied by different kinds of alteration (for example potassic or argillic alteration) ...


15

I think Azzie's answer describes the situations where gold is formed and found as Lode deposits. But native gold in lode can then be subject to weathering when it is exposed, which releases the gold into the environment as flakes, grains and nuggets. This gold is then subject to erosive and sedimentary processes. As gold is denser than most minerals it can ...


14

I'll take the form of the question given by another person here and attempt to provide a different answer. So what you are asking is: "How did gold become so concentrated in certain parts of the world?" So yes, gold is all around but the concentration is too low to make extraction of it worthwhile. You need some process to take small amounts of gold from a ...


14

I wouldn't say there's 'almost none' in Europe, but the global distribution of petroleum is uneven. The reason is that petroleum systems need a convergence of conditions that is relatively rare. For a start, the comment about the inappropriateness of a political map for this purpose is spot on. This USGS map of global petroleum systems, and non-petroleum-...


13

One example of an ore deposit that runs under a city is the banded iron formation ore in Kiruna. In this case the ore has been mined outside of the city since the turn of the previous century. The ore has been found to run under the city and there are now plans to move the city more detailed information. This has led to a process where the city has to be re-...


13

In addition to the above, what happens is that people look for commonalities between known deposits. So, for example, if you have a lot of gold veins in one area, and lots in another area, then you look at what is needed for these veins to form. Once you have a reasonable idea of possible ways to form your ore, then you have something that you can look for. ...


13

Helium is produced by the radioactive decay of primordial uranium and thorium. It should not be strongly associated with non-primordial 'fossil' hydrocarbons. The first statement is correct. The second is not. There are several reasons that helium should be strongly associated with non-primordial hydrocarbons. Both are fluids found predominately in the ...


12

The efficiency of coal as a source of electricity is very low: typically of the order of 30%. So losses are of the order of 70%. But losses due to energy expended in the extraction of the coal itself only form a very small proportion of this. Estimates for extractive losses tend to be of the order of 0.5-5%. That's a huge relative range, because the energy ...


11

I've been looking for these things over a few decades and along with other geologists doing this we have seen how we find things change somewhat. Many methods used a century ago are still in use, but with the addition of refinements. So looking at how large and small deposits were found will change over time. (Simple example of that would be that Romans and ...


11

First of all, Earth is not a random assortment of atoms. While it probably formed along like that in the beginning, somewhere along the way it differentiated into distinct core, mantle and crust, which are not chemically the same. That's a story for another question though, and there is an excellent answer to it on this site. Back to your question, Why are ...


11

"Rare earth" metals consist of Scandium, Yttrium, and 15 other metals of the so-called "Lanthanide" series toward the bottom of the Periodic Table of elements. Basically, these are the chemicals that we didn't study in chemistry class at school. Like other metals, they have two electrons in the outer shell, but unlike "metallic" chemicals such as sodium or ...


11

You are looking for a portable XRF. It does (almost) exactly what you said. It sends electromagnetic radiation to the rock (X-rays), which excites electrons in the atoms and when they bounce back they return X-ray of different energies which are detected by the instrument. It looks like this, for example: Using the different peaks you can figure out what ...


10

I've heard that gold ore is often associated with quartz veins. What geological processes enable gold particles to naturally cluster together like this? First of all, gold is mostly found in quartz veins in and around igneous intrusions. It happens with a very hot hydro-thermal fluid of silica, oxygen and concentrated gold that is created during ...


10

A few elements to complement @Siv answer, and some alternatives hypotheses: Originally the idea was that the Fe2+ oxidation into Fe3+ that lead to the formation of the BIF ("banded iron formations") was an indirect consequence of the increased atmospheric pO2 caused by the photosynthetic activity of, then freshly appeared, cyanobacteria (see e. g. Cloud ...


9

Diamonds are expensive. Really expensive. Even "cheap" synthetic diamonds are orders of magnitude more expensive than conventional fossil fuel. By using them as fuel, you will increase demand, thus increasing their price even more. And synthetic diamonds have to be made somehow, and you need energy for that. Diamonds burn, but they don't burn well. For ...


8

What are the rare earths? The rare earths are a group of several elements. The widest definition includes the 15 lanthanides: La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, and two more elements: Sc and Y. A quick look at the periodic table gives a hint as to why Sc and Y are also considered as REE: (modified from this) I've marked all the ...


8

The composition of Moon rocks is pretty much the same as that of Earth. However, none of the processes that concentrate specific minerals in one location (i.e. into a mineral deposit useful for mining) exist on the Moon. This is due to the lack of tectonic activity. Therefore in the Moon you would expect the rocks to be much more homogeneous than on Earth. ...


7

The answer depends a lot on what you mean by "excluding shale oil". Tight oil production, commonly referred to as "shale oil" is about 4 million barrels per day currently (2014), compare to almost none in 2005. Canadian oil sands production is at 2 millon barrels per day, compare to about 700,000 per day in 2005. So compare to 2005, tight oil (shale oil)...


7

The map shown in the question is of proven oil reserves that can be extracted under current conditions. However, it is really showing you the distribution of oil reserves in a political sense, which is not fundamental to the source of petroleum reserves. Instead, you should look at the geology that is responsible for oil reserves. I like the description ...


7

David Hammen's answer explains why He is extracted from natural gas. But, it is not found only there. Helium exists just about everywhere on earth. You find it in volcanoes, in subseafloor hydrothermal vents and even just slowly leaking away from the ground in U and Th rich zones. As with all extraction of natural resources, it comes down to economics. How ...


6

At μ/g level some decade ago, they were explained as forming in relation to the oxygenation of the atmosphere, as photosynthetic life developed changing a reducing environment to an oxygenated one, iron oxides formed precipitating out of seawater in variable bands related to local (or possibly seasonal) oxygen availability. Though this traditional ...


6

The simple answer is that the Earth is dynamic, e.g. plate tectonics. This wikipedia article on ore genesis is a good place to start, http://en.wikipedia.org/wiki/Ore_genesis . Ore genesis theories generally involve three components: source, transport or conduit, and trap. This also applies to the petroleum industry, which was first to use this ...


6

It is unlikely anything other than salt would be derived from sea water. The largest deposit of gold is dissolved within the worlds oceans - in terms of tonnes of metal. The problem with extracting the gold from sea water is the concentration is so low it is uneconomic to do so. It's why we keep mining hard rock sources of most metals. This problem exists ...


5

According "The youngest natural oil on earth" Doklady Chemistry vol. 438, pages 144-147: Prior to this paper, it was known that oil of the Guaymas basin is from young sediments and is 5000 years old. However, their work shows that oil in the Kamchatka volcanic area is "less than 50 years old". Oil is shown through carbon dating to have formed between 1962 ...


5

Adding to Sabre Tooth's summary: In addition to weathering of felsic volcanics as ST describes, another aspect that has received attention over the years has been direct input to the salar (or playa) from hot spring sources. The idea being that the lithium is coming in as magmatic, not just meteoric water. There is no question that hot springs are ...


5

Gold has primary origin in hydrothermal veins and contact metamorphic deposits and pegmatites. Also occurs in placer deposits of secondary origin. It is more easily found in veins that is related to igneous rocks rich in silica. The main sources of gold are in hydrothermal quartz veins with pyrite and other sulfides. Gold is mechanically mixed with ...


5

Impact diamonds Yes, diamonds can form in meteorite impacts. For this several things need to happen: A meteorite of the correct size and velocity, The stuff it hits needs to contain carbon. If you have a meteorite hitting granite or ocean you're not going to get any diamonds. It usually has to hit something that has biogenic carbon (let's say peat, coal, ...


Only top voted, non community-wiki answers of a minimum length are eligible