Surfacing: new chum asks

[Metabet]

Standing atop a gully in a heavily investigated (for gold) Victorian bush landscape, behind is a dam dug in the late 1800s/early 1900s for surfacing the gully. I understand the old-timers used high pressure water jets to remove the top soil to reveal any surface gold. Question: did they try to expose nuggets below the top-soil which remained stuck in their original position, on the hill-side, or did they blast all the dirt to the bottom of the gully to sift through it there, or something else? At the bottom of the gully, next to the creek, the ground rises unnaturally. I was surprised that if you dig through the surface topsoil there is another layer of vegetation. I think the soil I dug through first was the soil driven down the hill, which over 100 years eventually compacted and grew grass of its own. A false surface covering the original. I'm thinking of detecting the hidden original layer. I assume that in surfacing, the top of the gully was worked first and not bottom up. Question: any of this sound 1/2 right? Thanks in anticipation.

 

[grubstake]

Standing atop a gully in a heavily investigated (for gold) Victorian bush landscape, behind is a dam dug in the late 1800s/early 1900s for surfacing the gully. I understand the old-timers used high pressure water jets to remove the top soil to reveal any surface gold.

You're conflating two different mining methods:

Surfacing involves removal by pick and shovel of relatively shallow gold-bearing dirt for treatment elsewhere in a washing plant (typically a puddler), to recover any gold in the dirt. Most surfacing stops at red clay, rather than actual bedrock, except in what was naturally very shallow ground. Surfacing was used where water was scarce (eg. the Victorian Golden Triangle).

Hydraulic sluicing is the process of using high pressure water jets to flush all dirt and gravel above bedrock, downhill though sluices set up at the lowest point of the mined area. Hydraulic sluicing needs a lot of water, which would need a pretty big dam. It was mostly reserved for goldfields with deep alluvial ground and plenty of running water (eg. NZ, California).

Question: At the bottom of the gully, next to the creek, the ground rises unnaturally. I was surprised that if you dig through the surface topsoil there is another layer of vegetation. I think the soil I dug through first was the soil driven down the hill, which over 100 years eventually compacted and grew grass of its own. A false surface covering the original. I'm thinking of detecting the hidden original layer. I assume that in surfacing, the top of the gully was worked first and not bottom up.

The only accurate way to know what the mounded ground represents is to test it by panning. It may be just the dirt that was excavated for the dam.

 

[Metabet]

Thanks, that's a big help.