Trace Minerals found with Gold

Forward:

There are many minerals that are found in nature with gold, one of the most common found in placer deposits is small grains of magnetite.  This and other minerals have been used to find gold that can be recovered by the use of the pan.  Other minerals have been used in locating gold in lode deposits.  It seems that gold is often found with other metal bearing minerals including iron. These are called indicator minerals.

Fig. 1 Crystalline gold

Placer Deposits:

Placer deposits are made from the products of erosion if they can withstand the rigors of the weathering process.  Very few minerals are hard and tough enough to survive whole and remain recognizable when they have been reduced to the size of sand grains, around 2 mm in diameter.  The most abundant mineral found in sand is quartz, SiO₂ also known as silica. 

Quartz grains along with other minerals having a hardness of 7 or more on the Mohs Scale of Hardness make up what are called black sands or stream heavies in placer deposits.  Gold is another mineral found in the same environment that doesn’t depend on its hardness to survive in such an environment instead quite the opposite is true.  The ability of gold to survive is its softness and malleability allowing it to survive in placer deposits.

Most of the indicator minerals for gold are . . .

Quartz	Magnetite (Magnetic)	Hematite
Garnet	Beryl	Corundum
Feldspar (Sometimes)	Kyanite	Sillimanite
Topaz	Tourmaline	Mica (Small flakes)
Diamonds	Monazite	Zircon

There are others in the list, but these are the most likely to be encountered.

Lode Gold:

Lode gold is found in solid rock that is often discovered by tracing placer gold back to its source often using the indicator minerals found associated with gold in the gold train, a scattering of gold found away from its source rock.  The further away gold is from its source the smaller the particles become and the more widespread the individual particles of gold become.

Fig. 2 Gold in quartz

Most gold is found in quartz veins where it has been deposited from hydrothermal waters into the older quartz veins.  Much gold has been found in iron pyrite as a contaminant, and ever rarer it is sometimes discovered a “telluride” where it is combined with the element tellurium.

Many of the same minerals as found in sand can also be found in occurances of lode gold, but there are several other minerals that are just too soft to survive the rigors of weathering, they include . . .

Apatite	Calcite	Biotite Mica
Galena	Sphalarite	Chlorite
Feldspar	Staurolite	Arsenopyrite
Amphobolite	Garnet	Iron Pyrite
Pentlandite	Argentite	Granular Magnetite

These are the most common minerals associated with lode gold; there are others.