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How do large gold ore heaps allow cyanide solution to reach the gold?

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A worker in safety gear walks beside a conveyor belt carrying ore at the Tanami gold mine in the arid, expansive landscape of the Tanami Desert. — gold processing The Tanami gold mine, Northern Territory, Australia.

In the context of gold processing, large gold ore heaps allow cyanide solution to reach the gold through a process known as heap leaching.12

To prepare for this, low-grade ore deposits are first shattered by explosives and then piled into large heaps, which can reach hundreds of meters in length and up to 30 meters in height. Once the ore is piled on pads, a dilute solution of sodium cyanide is sprayed over the top of the heap.312

The solution then trickles or percolates downward through the piled ore. As it moves through the heap, the cyanide solution dissolves the gold contained within the rock. The resulting gold-bearing liquid, often called the pregnant solution, is then drained away from the base of the heap and collected for further processing and gold recovery.12