Shale has long been used by humans for purposes like making pottery and bricks. But could the humble shale also contain valuable materials like gold?
While shale itself does not contain significant amounts of gold, there are a few ways that gold can become associated with shale deposits. First, it's possible for rivers to erode particles of gold from upstream gold-bearing rocks and deposit that gold within shale sediments. However, the amount of gold accumulated in this manner is usually very small.
A more promising way for gold to occur in shale is when the shale gets invaded by an igneous intrusion. When magma from below the surface intrudes into shale beds, the heat and fluids from the magma can alter the chemistry of the sediments and concentrate valuable metals. Under the right conditions, the intruding magma may provide a source of gold that can then disseminate into the surrounding shale. Skarn deposits that form at the contact between shale and intrusive rock are one example where gold mineralization can occur.
The other major way for gold to enter shale formations is through hydrothermal fluid flows. As hot, metal-rich fluids circulate through the crust, they can permeate into shale layers and precipitate out gold and other metals by interacting with the chemical constituents in the shale. Organic-rich black shale is especially favorable for hydrothermal gold deposition because the carbon acts as a precipitant for the gold. There are many gold deposits hosted in black shale, with the Carlin Trend in Nevada being one of the most famous examples.
While shale does not have an inherent abundance of gold, geologic processes like igneous intrusions and hydrothermal activity can introduce gold into specific shale units. Prospectors and geologists look for key signs that point to these types of gold enrichment when exploring shale formations. Features like intrusive dikes, carbonaceous content, and geochemical anomalies help identify which shale beds are worth evaluating for their gold potential. While hit-or-miss, shale can be an important host rock for gold in the right geological environment. Careful scientific investigation and analysis are required for determining if an unassuming shale unit might be hiding valuable gold resources within its subtle layers. With the right insights, even the humble shale could give up glints of shiny precious metal.
