Nuggets of News Blog 

You might think that glaciers are important to gold prospecting only in Alaska and the Yukon, but glaciers have also affected placer deposits in the Midwest and some western states, too. 

What is a glacier?

Glaciers are formed when a huge mass of ice is created by accumulated snow. The body of ice grows over the years when more snow falls during colder months than melts during warmer months. Glaciers shrink when the melting is greater than the snow accumulation. Once the weight of the glacier grows large enough, the weight of the snow and ice presses down and compacts. The body of ice will then slowly flow downhill. The power of the solid ice moving downhill rips loose rock and soil. Solid rock underneath the glacier that is firmly attached to the mountain will stay in place, but be polished and smoothed as the glacier slides over it. Scratch marks and gouges appear along the surface of these polished rocks and indicate the direction that the glacier was moving.

Eventually the body of the glacier reaches a warmer elevation where the ice melts more easily. Here, at the foot of the glacier, are gigantic piles of rocks and boulders and debris that have been bulldozed down by the moving massive glacier. These glacial gravels are known as “moraines.” However, finding gold in this unsorted jumble of glacial moraine material produced by a glacier’s bulldozing effect is like finding a needle in a haystack—not worth the time to process…. until the glacier’s natural melt waters or another water source washes through it, and does a bit of natural sorting.

Alluvial gold deposits

Normal alluvial placer deposits form by the power of flowing water washing away lighter materials and gravels and leaving behind heavier material such as gold— very similar to what happens in a sluice box when the flow of water washes away the lighter materials and the gold is deposited in the riffles.  When flowing streams and glacier melt water process and wash away the glacial moraine gravel, the gold works its way downward.  Gold will then be deposited on bedrock or false bedrock (such as clay or other packed material). As the glaciers themselves melt, the huge quantity of water creates an effective sluicing system that can sort the gold out of gravels. These flows can leave behind very profitable pay zones along the channels cut by the ice melt waters on bedrock benches, among packed false bedrock gravels, and on the downstream side of bedrock high spots.

Where to look for glacial placer gold deposits in the West

In California, glaciers still exist in the southern Sierra Nevada, small parts of the Cascade ranges and the Shasta-Trinity Alps. In the northern Sierra Nevada and higher parts of the Klamath and Trinity ranges, that area’s placer deposits were greatly affected by glaciers that existed thousands of years ago. Glacial derived placer gold is important in a number of other western states, too, including Idaho (Boise Basin and Mount Pisgah), Montana (Pioneer District, upper portions of Gold Creek near Deer Lodge) and in Colorado (Fairplay District, Arkansas River Valley in southern Lake County).

Where to look for glacial placer gold deposits in the Midwest

What you might be very surprised to know is that glaciers are the source of nearly all the placer gold found across the Midwest. During the past ice ages (which were repeated events, not just a one-time occurrence), great sheets of glacial ice leveled the middle parts of North America, acting like giant bulldozers by pushing enormous amounts of material southward from Canada. When the ice melted, the area was left with extensive glacial moraine (gravel) deposits. Although it’s spotty and sporadic, some of these glacial deposits have gold, depending on where the glacial gravels came from in Canada and if that region was gold-bearing. Glacial gold is found in several of the northeast states such as New York, Vermont, and Pennsylvania. Glacial gold is also found more extensively in Midwest states such as Indiana, Illinois, Ohio, Michigan, Wisconsin, Iowa, Minnesota, Kansas, Nebraska, Missouri and the Dakotas.

All things considered, while glaciers can destroy a placer deposit, the moraines they leave behind can produce some very worthwhile deposits of gold, and are worth prospecting if you live in or visit these areas.