Sometimes in mountainous mining areas, there will be mines way up on a steep cliff. Sometimes they are in places which would be difficult to hike up to, much less carry heavy mining equipment and dig through all that rock. What indication did the miners have that locations like that would have potential for gold or whatever? Did they just spend all day climbing steep terrain digging holes hoping to find something? Or did they pick up on clues on at the bottom which lead them to believe that hundreds of feet up the cliff face would be a good place to mine?
I’m guessing they would first look at what was at the bottom and see is there was gold there, assuming there wasn’t a river and the gold couldn’t have washed down from somewhere else.
Miners became very proficient at using high pressure water to wash down the sides of cliffs and then sluice the gold that was there.
You could send someone up the cliff face, drill a hole, put in a stick of dynamite with a long fuse and see what comes down after the blast. There are a number of ways to test for the presence of gold in fairly inaccessible places.
Right … erosion would cause some for the gold to wash down into the gully … one need only follow the “treasure trail” up to the source and dig the mine …
Maybe they saw actual traces of the ore veins in the side of the cliff.
If I saw gold reflecting off the side of a cliff I would consider that to be an excellent place to start mining.
You see a hole when you look at their results but the miners may have seen the actual ore on the cliff face.
Mark Twain on pocket mining.
I was 4-wheeling with cousins in an area with old mines several years ago.
Steep, hot, dry canyons. At least that time of year. Bitterly cold for months at a time. Yet people worked mines in those canyons. Some fairly high up the sides.
I am amazed what people did 100+ years ago for gold.
Gold, silver, or gemstones!!
The general term is called “float” ie its what comes downhill, from cliff faces, and gives an indication as to whats up higher. Telescopes and other scopes can be used as well, to spot anomalies, pockets, or markings indicating different rocks meeting etc etc.
Minerals such as gold or silver have to be found in really high concentrations to make it worth going up (and down) cliff faces, especially if its not loose pockets, but is veins in hard rock. Gemstones, on the other hand, can form in very small pockets high up on mt faces, and those can(were) worth the time and effort.
I recall reading that even today, a fair amount of people die each year in the swiss, german, and italian alps regions, climbing cliff faces in search of gemstone pockets.
I’ve done a fair amount of easy climbing in california mountains looking for hand specimens, as I wanted to find and cut the stones myself.
The weather channel has a yearly show called prospectors, showing folks in the Mt. Antero region of Colorado looking for gemstones and also a bit of prospecting for gold and silver.
Some of the areas of California where the water cannons were used are really weird looking, piles of rock and gravel where they shouldnt be, and streams running in some really peculiar ways. Some areas were close to 100% washed for gold, it amazing there is ANY topsoil of plants left at all.
Clues would be any rock indicating there has been magma /vulcanism affecting the rocks.
The larger amount of metamorphic material the better.
Types of quartz deposits that are indicating that the quartz has deposited out of ground water would also indicate the possibility of gold, the gold will be in that quartz.
Thats why they know they are getting a few grams a tonne from “ore”, they know its a quartz deposit ore and its quartz that has dissolved out of other rocks.
Better if there is an abudance of metamorphic granite type rocks ?
Any gold present in the rocks being heated and squeezed is sweated out and goes into solution as complex ions. In this form, dissolved gold, along with other elements such as silicon, iron and sulphur, migrates wherever fractures in the rocks allow the fluids to pass. This direction is generally upwards, to cooler regions at lower pressures nearer the Earth’s surface. Under these conditions, the gold eventually becomes insoluble and begins to crystallise, most often enveloped by masses of white silicon dioxide, known as quartz. This association of gold and quartz forms one of the most common types of “primary gold deposits”.
For gold, and some other precious metals, because they’re usually associated with sulphides, iron staining (gossan) can be a good clue.
Even with the clues, it still seems remarkable they found the places to mine in the first place. Some of the mines are pretty remote even today. It’s hard to believe people were hiking around in these mountains a hundred years ago trying to make a living. It seems like it would be an incredibly hard life.
You can see the effects of vulcanism in the cliff face. You can find the affects rocks , or erosion from them, below, and follow that up. You can see the layers where the more recent vulcanism has caused some changes, you can see the fault that the magma came up through as steps in the layers of the rock…
and basically people panned rivers and followed the gold in the rivers up. If they found a gold bearing river, they could follow it up to where the gold is eroding from the cliff face…
All comments so far have been on metals, but in sedimentary geology you may well get rich seams of coal or other products.
Although there may be effort required to access a seam half way down a cliff face, this is probably no more than needed to remove overburden from above and sink drives. Once you are at the right level, you simply punch adits in.
Also in mining, height is good and gravity is your friend. If you can push stuff out and gravity can take it down a chute / trolley line / ramp to the valley floor works then thats tons and tons you don’t have to mechanically lift.
The coal mines and oil shale mines around the Sydney Basin are all in largely flat strata. Many were initially accessed via cliffside entry, and relied on gravity to move product to valley bottoms for processing before the value-added material was moved for sale.