The "mother load" seems to have been a deposit of some sort on top of the Bradford Woods ridge (in Morgan county), another large deposit on top of the second highest elevation in the region called Mt. Nebo, and the highest called Weed Patch Hill (all in Brown county).
Early miners simply tossed shovel loads of soil off the side of the hill and the rain would wash off the lighter materials and the heavier stuff would eventually slide down the hill where it could be readily extracted through very simple mechanical means.
They didn't need to use cyanide in this process.
The fact that so much of the lode was on the tops of hills led early researchers to assume the glaciers, which stopped near here repeatedly through many ice ages, left the diamonds and gold as they retreated.
At the same time Mt. Nebo and Weed Patch Hill were NOT inundated by ice. The valleys in the formations in Brown County were cut by running water, not ice. There turns out to be little glacial till even half way up these shale hills.
Further South in Jackson and Clark counties, where there were glacial hills called "knobs", there were little or no deposits of gold and diamond. Closest thing to that were the fools gold (iron pyrate) and native copper deposits that could be found in the early pioneer period.
Folks who'd observed the anamolous distribution of the loot wondered if maybe it hadn't just been dropped out of the sky!
Here, you'd have low trajectory diamond laden ejecta raining down on hills, valleys and everywhere in between.
As the great glaciers melted at the end of the Younger Dyras, they created a massive river that worked its way back and forth across Indiana for several thousand years destroying all in its path. The only places that weren't washed away were the tops of the shale hills, and that's right where the gold, silver, diamonds and other neat stuff was found.