A specific rock type is not necessarily a good indicator of gold presence. It is true that gold and quartz often travel together, but quartz is the second-most common mineral on the planet. So finding quartz does not indicate gold. But when you find gold, quartz is often there too.
I wrote a Gold Prospecting Field Guide that explains it. Check out my website, click the globe icon in my profile.)
The way gold is formed deep in the Earth is the same as many other minerals, especially heavy minerals (metals like silver, iron, lead, etc.). These are then forced up through cracks in the rock, and when they cool, they form mineral veins. Quartz is a hard crystal, so it fractures easily, making it a good host for gold and silver veins to form.
So what you are looking for is rock that has a lot of mineralization: dark, rusty, corroded looking. The more mineralization, the better the odds that gold is one of them. That could occur in igneous (volcanic) rock, or metamorphic rock (like granite). A lot of miners make the mistake of assuming those are the only places to find gold, and that is not true.
As those rocks erode and fall apart, they eventually wind up in a river. Because these are heavy minerals, they tend to collect in the same areas. Over time, they can become a part of sedimentary rock.
When I am scouting a new area, I use my metal detector in and out of the river. It will detect gold flakes, but most river gold is too fine to locate that way. Instead, I watch for lead (bullets, fishing sinkers, birdshot, etc.) or iron. Since they are heavy, the places they collect are the places where gold will settle because gold is twice as heavy as lead.
So how do glaciers fit in? North of the area I am looking at are many mines that were the state's top gold producers. They are under claim, so I can't mine there. They are mining the gold veins in the rock. When the glaciers came through long before those mines were there, the ice scraped those rocks and the bedrock below, and pushed that material into an area where I can prospect. So, I look for the edges of the moraine and where that till was piled up. It turns out that people have been digging gold out of that ground since the 1870s and are still doing so today. I want to be one of them.
😁