Sulfide minerals can provide important clues for small-scale gold miners and prospectors in locating both placer and lode deposits. This is especially true when it comes to lode or vein gold. The following are some of the main sulfide mineral indicators you should keep an eye out for when prospecting.
Bear in mind, mineral indicators are only clues that gold MAY be present. However, while not guaranteeing the presence of gold, they strongly suggest it.
The main sulfide mineral associated with tin and the biggest matrix for tin ore. It is typically found in igneous and metamorphic rock formations. The old timers knew the significance of sphalerite as a potential gold indicator and called it “blackjack” or “rosin jack.” Sphalerite comes in a range of colors, including grey or greyish-black and usually has a metallic luster.
The main sulfide ore of copper throughout the world. And where’s there’s copper there’s usually some silver or gold found along with it. Chalcopyrite is typically a brassy yellow in color and when exposed to the elements loses its metallic luster. Its surface then becomes rough or granular. Sometimes chalcopyrite can have an iridescent look with multiple colors across its surface which is why it is sometimes referred to as “peacock ore”.
The main lead ore, galena is essentially lead sulfide. Galena is easy to spot since it usually displays a silvery gray color and if broken will show perfect cleavage in three directions. Galena will oxidize or “tarnish” to a dull grey when exposed to the elements. It has a specific gravity of around 7.5, which makes it fairly heavy and dense. In crystalline form galena exhibits cubic crystals. It often contains small amounts of silver.
Bornite is another important ore of copper. Bornite is metallic in its appearance and displays a copperish-red color until exposed to the elements. Then it will turn an iridescent violet color, or sometimes a pale pinkish-gray.
Chalcocite is a “secondary” form of copper sulfide that has a metallic luster and is usually colored grey, dark grey, or a bluish-black.
Almost everyone is familiar with pyrite. Commonly known as “fool’s gold” pyrite (iron sulfide) forms in cubic crystals that can range in color from brassy yellow to silvery. It invariably displays a metallic luster which is why it’s often mistaken for natural gold when found in brassy yellow color. A big difference between natural gold and pyrite is that real gold will maintain an even, lustrous glow when exposed to direct sunlight while pyrite will “flash” or sparkle. It also has a high specific gravity which is another reason its often mistaken for natural gold. However, the presence of pyrites is often a good sign you may be in an area of gold mineralization.
These are the main mineral indicators of the possible presence of lode, and sometimes placer, gold in a given area. Once again, they aren’t guarantees, but these sulphides are very good indicators that gold will also be present.