Tuesday, April 1, 2014

Placer mining in Montana a classic catastrophic debris flow

Bear Creek Montana a classic catastrophic debris flow
Our placer mine in Drummond Montana. Debris flows.  

Sometimes you are in the right place at the right time.

To get a better grasp of a catastrophic  geological event I was at was that right place. I witnessed a terrible geologic landslide event in 1999 100 kilometers north of Caracas Venezuela. I was retrofitting an airlift suction dredge on the Caroni River in central Venezuela when this event occurred. I heard about the great loss of life and the destruction near the international airport of Maiquetia Venezuela. I was on my way to the airport to pick my buddy Dick Simpkins who was coming down to work for me. Nothing could have prepared me for the destruction I witnessed. The landslides completely destroyed the town of Ceaballeda. The loss of life was estimated at 30,000 people. Dick and I clambered about the devastated city, stood 4 stories up inside of the hotels that were destroyed,mud and debris filled.

I immediately  recognized firsthand what a debris flow was all about. The characteristics of landslides initiating on steep tropical weathered sloping hillsides laying on exfoliated rock was what I was about to experience first hand,  it gave me a real blueprint as to what shaped a mining project I worked on in Montana a few years later. Heavy heavy rain falling in a short time triggered mudflows and landslides that quickly transformed into debris flows. Of note was the channel and alluvial width, the steep gradient that carried rocks as big as busses.  This flowed all the way to the ocean. The rock and mud media enabled the jumble of boulders to be swept down the valley floor.
The boulder matrix was unsorted and unstratified.

I have noted a similar event  on the Bear Creek drainage near Drummond Montana. It was in all probably  the same kind of catastrophic debris flow event. A debris flow of this type, suspends the boulders within a matrix of mud and smaller rock that created a  media density.This media came from the headwaters of the valley and happened to be auriferous with gold from the lodes scattered at its headwaters. This is an assessment in general I am making to answer  nearest I can tell about the boulder deposition along the Bear Creek drainage.

A friend was hydraulic mining a small section and you can see without a doubt how the matrix of rocks and boulders was placed so far up the banks along the entire drainage