Three Rocks that Contain Gold
For thousands of years people have been chasing after gold. Finding gold has been a part of life for many civilizations for centuries. Rocks are obviously where you find gold, but many do not know much about rocks to know which rocks might contain gold.
Gold is contained within the three main rock types; Sedimentary rock, metamorphic rock, and igneous rock. All three rock types are known to contain some amounts of gold. Sedimentary rocks are often thought of containing the most gold.
In many cases gold will end up in rocks by the hydrothermal process. Cracks and openings in rocks were filled with heated ground water. This hot liquid was pushed from below into these cracks filling them with its contents, including gold.
Sedimentary Rocks
Sedimentary rock will usually contain the most amount of gold. The reason for this is due to metamorphic and igneous rocks parting with their gold, into sedimentary rocks. This can be done by the hydrothermal process as well as erosion and weathering of igneous and metamorphic rocks.
Weathering and erosion of igneous and metamorphic rocks containing gold, will deposit those contents in rivers or even sediment in lakes. This can create greater concentrations of gold in sedimentary rock.
Many have heard the term panning for gold. The gold found in the sediment of river beds came from the breaking down of rocks. Since gold is heavy, it stays put for quite some time in many rivers. This of course allows people to access the gold without having to go mining for it.
For some more detailed information on sedimentary rocks, I have an article you might be interested in reading “What Are Sedimentary Rocks”.
Metamorphic Rocks
I often don’t really think of metamorphic rocks as containing gold. Metamorphic rocks are rocks that did not quite reach a melting point, but “changed” due to tremendous amounts of heat. Gold can often be contained within metamorphic rocks, but may not be visible.
Metamorphic rocks that contain gold may contain less than 1 PPM to up to 20 PPB. I know that does not mean much too many. PPB is parts per billion, and only 20 is pretty small and likely not worth attempting to get at. Or at least it is not cost effective.
Most metamorphic rocks that contain gold do not contain even up to 5 PPB. So this puts metamorphic rocks at a place where people would not be interested in retrieving its gold.
For some additional detailed information on metamorphic rocks, I have an article you might be interested in reading “What Are Metamorphic Rocks”
Igneous Rocks
Igneous rocks are metal bearing rocks, including gold. Gold found in igneous rocks are often visible to the eye. Quartz rock is often the rock thought of when it comes to a rock containing gold.
Quartz veins are places within quartz where gold can accumulate and concentrate. This leads to larger looking pieces of gold. Though sedimentary rocks can have small chunks of visible gold, it obviously pales in comparison to the beauty of that gold gleaming at you from some quartz rock.
Much of the gold that is panned in rivers has been broken off from larger gold deposits up river, usually attached to some quartz. I am not a gold prospector, but as a rockhounder I wish I could stumble onto one of these quartz/gold beauties and add it to my collection.
For some additional information on igneous rocks, I have an article you might be interested in reading “What Are Igneous Rocks”. These types of rocks are my favorite, as they can contain some really great minerals.
Identifying Rocks that Contain Gold
Most rocks cannot be identified as containing gold, even though many of them do. Quartz rocks containing gold can easily be identified because you can actually see the gold. Large quartz rocks containing visible gold are often desired by rock and mineral collectors.
For rocks where you cannot see the gold there is a process of extraction. This usually requires breaking up the rocks, doing measurements, and using heat. Once you have some gold, you can calculate how much of it you have, compared to how much rock you extracted it from.
If there is enough gold extracted, it may be worth continuing to extract it from that gold ore.
Not Just Rocks but Minerals Can Contain Gold
Calaverite and sylvanite are minerals that contain gold. There chemical formula makeup includes the element Au. Sylvanite will contain around 34% gold, calaverite will contain around 43%.
These two minerals are almost the same in chemical composition. What separates them as two different minerals is the content of silver. If there is less than a little over 13% of silver, replaced by gold, then it is considered calaverite.
Many other minerals can contain amounts of gold in them. Though they may not be part of the chemical makeup of the mineral, they may present in the mineral as an impurity.
Pyrite is a good example of this. Though pyrite is often called fool’s gold, it can actually contain gold. At times, if the contents of gold is high enough in pyrite, it will be extracted. Keep in mind the ratio of gold to current price of gold, as your cost to extract may exceed your profit!
Pyrite is a wonderful mineral that many people especially kids love to collect. I have written a great article on pyrite “All About Pyrite” including information and pictures.
Conclusion
All three types of rocks can contain gold; Sedimentary, Metamorphic, and Igneous. The most commonly known rock to contain gold is quartz rock and this is due to the visibility of the gold within the rock.
Many of the other rocks will not have such visibility of their gold contents. The only way to know if it is gold bearing is to run the rock through a processing to find out.
Various minerals will also contain gold. Some will have gold as their chemical makeup and others will not.
Gold after many years can move around in these three types of rocks. That movement occurs in what we call the “Rock Cycle”. For reference on this you can see my article “Diagram of The Rock Cycle” which describes in detail the process of the rock cycle.
