Sampling
Nov 11, 2008 8:50:14 GMT 12
Post by RKC on Nov 11, 2008 8:50:14 GMT 12
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Recommend Message 1 of 1 in Discussion
From: Roscoe (Original Message) Sent: 3/03/2007 6:31 p.m.
I thought I would post an article from the other forum (now closed). Pull it to bits by all means.
From: Roscoe (Original Message) Sent: 15/10/2006 4:47 PM
Since visitors are slow to post, I`ll talk to myself till it happens.
Most dredgers I`ve watched tend to either use the old methods of starting a suck--(a) follow the book illustrations, do behind rock bars, boulders, river bends,etc., or (b) have a hit-and-miss go by tackling any spot that seems nice. A few even believe in taking up the whole stream (c) on the notion that they will eventually hit the jackpot.
Now (c) might be o.k. if you are working a very narrow side stream, or tackling a waterway where exposed bedrock narrows down the amount of ground to be processed.
(b) is an intuitive thing that might work if you have been in the game for years and subconsciously figure out the most likely spot.
(a) is the logical method, except for one thing. In this day and age, it is getting harder to find a stream that hasn`t been hammered in the past--in precisely the same areas that you are tackling. Flood gold can partly replenish old workings IF the stream is subject to really heavy floods, sufficient to bring down landslides, or rip up the existing bedload of boulders and gravel and re-concentrate gold deposits. Mere occasional floods will sometimes drop a thin layer of fine or flaky flood gold, usually on top of a clay layer.
So where do we go to stand a chance of getting a few ounces? Remember that most streams in Australia have been worked by the old timers in normal water heights as well as in drought, followed by recreational or semi-pro dredgers years later. Some rivers were worked by bucket dredges for a considerable time.Very few rivers were of such a depth as to block determined miners. Streams that dried up into a string of waterholes were drained by buckets and the bottom cleaned. The answer is to concentrate on the gaps that got missed by the miners before us. If we strike a patch while doing it, well and good. The areas to concentrate on are:
Overlooked areas--where drought or poverty or the call of a new gold field forced the originals to move on. These can sometimes be picked up by the unsorted areas of river gravel, gravel which is still in a mixed state, long stones still aligned with the old river flow, perhaps even still cemented together. These can be underwater, on the banks, even a distance away if the waterway has changed its course.
Under processed places--rockers and even sluices arena`t rated that high in the gold processing game with considerable losses if the operators arena`t experienced. And many of the old timers were new chums. If you see tailings heaps, run a few quick samples from various heights in the pile. 'Who knows? is our motto, till proven wrong.
False bottoms have a weird history, prevalent in some areas depending on the composition of sediment moving downstream, and next to non-existent in other areas. Watch for different colors, textures,even odd shapes. Especially watch for pudding-stone--river pebbles embedded in the supposed bedrock. The ones I`ve seen almost blended into the bottom, just a scab on the face of bedrock and stained to match. If the gold in transition is coarse, maybe the scab will be shallow enough to let a metal detector react. Even a crowbar dropped at intervals might pick up a dead sound to give the game away.
Watching a river at flood time can change your summary of where the null zones are, and thus where the heavies drop. Some rivers shortcut in flood time, diving across a bend and dropping on usually dry land. When this happens sample where the shortcut re-enters the river. I found one rich creek even flowing up steam in flood time. Map the flood for calmer times.
Old river courses. In a narrow valley, the only way a watercourse can cut is down-wards, so keep an eye out for perched terraces. Wider streams can meander due to sediment loads blocking the old channel. Rounded river stones will usually give you a starting point. Follow those until you see some kind of bedrock to form a trap.
Idriess mentions boil-holes, and some rocks like granite, slate and shale can develop some beauties up to meters across. Usually, they have been done over. However chipping around on what seems like a solid surface occasionally opens up into holes or even concealed crevices. If they haven`t been worked before, you could get a nice surprise. Same with obvious crevices. If they are in the right position and have only been half-cleaned, do it and bar down the sides and bottom while you are at it.
Part 2
From: Roscoe Sent: 12/11/2006 8:48 AM
More of the same.
We know that heavier pieces of gold tend to find their way towards bedrock and, barring a blocking medium like thick clay layers, will do so. Likewise the denser minerals such as magnetite (black sand), tin, ilmenite, even rutile in certain districts. Certain gemstones like sapphires, garnets and zircons can show up in the null zones, too. So this gives us an indicator if we are trying to determine where gold Will be dropped in flood periods. Find the indicator mineral for that particular stream and you will know when you are working the most likely area. Of course, chasing indicators means you have to do regular cleanups or inspections to see whether you have crossed the drop zone. Rather than shut down a bigger production dredge, I prefer to power a small inspection dredge by inserting my jetter hose into a custom eductor jet, and using the suction to clean out the first few riffles on the main dredge without doing more than running clean water through the main dredge while removing the trapped concentrates. A two-man job, naturally. Having a mate monitoring the heavies keeps me on track if I hit a pay streak or indicator minerals. Shallow streams where I`m taking up all the overburden and base level gravels don`t need a constant check, but deeper deposits save time and money by letting you know when (or if) you are running hot.
Reply
Recommend Message 1 of 1 in Discussion
From: Roscoe (Original Message) Sent: 3/03/2007 6:31 p.m.
I thought I would post an article from the other forum (now closed). Pull it to bits by all means.
From: Roscoe (Original Message) Sent: 15/10/2006 4:47 PM
Since visitors are slow to post, I`ll talk to myself till it happens.
Most dredgers I`ve watched tend to either use the old methods of starting a suck--(a) follow the book illustrations, do behind rock bars, boulders, river bends,etc., or (b) have a hit-and-miss go by tackling any spot that seems nice. A few even believe in taking up the whole stream (c) on the notion that they will eventually hit the jackpot.
Now (c) might be o.k. if you are working a very narrow side stream, or tackling a waterway where exposed bedrock narrows down the amount of ground to be processed.
(b) is an intuitive thing that might work if you have been in the game for years and subconsciously figure out the most likely spot.
(a) is the logical method, except for one thing. In this day and age, it is getting harder to find a stream that hasn`t been hammered in the past--in precisely the same areas that you are tackling. Flood gold can partly replenish old workings IF the stream is subject to really heavy floods, sufficient to bring down landslides, or rip up the existing bedload of boulders and gravel and re-concentrate gold deposits. Mere occasional floods will sometimes drop a thin layer of fine or flaky flood gold, usually on top of a clay layer.
So where do we go to stand a chance of getting a few ounces? Remember that most streams in Australia have been worked by the old timers in normal water heights as well as in drought, followed by recreational or semi-pro dredgers years later. Some rivers were worked by bucket dredges for a considerable time.Very few rivers were of such a depth as to block determined miners. Streams that dried up into a string of waterholes were drained by buckets and the bottom cleaned. The answer is to concentrate on the gaps that got missed by the miners before us. If we strike a patch while doing it, well and good. The areas to concentrate on are:
Overlooked areas--where drought or poverty or the call of a new gold field forced the originals to move on. These can sometimes be picked up by the unsorted areas of river gravel, gravel which is still in a mixed state, long stones still aligned with the old river flow, perhaps even still cemented together. These can be underwater, on the banks, even a distance away if the waterway has changed its course.
Under processed places--rockers and even sluices arena`t rated that high in the gold processing game with considerable losses if the operators arena`t experienced. And many of the old timers were new chums. If you see tailings heaps, run a few quick samples from various heights in the pile. 'Who knows? is our motto, till proven wrong.
False bottoms have a weird history, prevalent in some areas depending on the composition of sediment moving downstream, and next to non-existent in other areas. Watch for different colors, textures,even odd shapes. Especially watch for pudding-stone--river pebbles embedded in the supposed bedrock. The ones I`ve seen almost blended into the bottom, just a scab on the face of bedrock and stained to match. If the gold in transition is coarse, maybe the scab will be shallow enough to let a metal detector react. Even a crowbar dropped at intervals might pick up a dead sound to give the game away.
Watching a river at flood time can change your summary of where the null zones are, and thus where the heavies drop. Some rivers shortcut in flood time, diving across a bend and dropping on usually dry land. When this happens sample where the shortcut re-enters the river. I found one rich creek even flowing up steam in flood time. Map the flood for calmer times.
Old river courses. In a narrow valley, the only way a watercourse can cut is down-wards, so keep an eye out for perched terraces. Wider streams can meander due to sediment loads blocking the old channel. Rounded river stones will usually give you a starting point. Follow those until you see some kind of bedrock to form a trap.
Idriess mentions boil-holes, and some rocks like granite, slate and shale can develop some beauties up to meters across. Usually, they have been done over. However chipping around on what seems like a solid surface occasionally opens up into holes or even concealed crevices. If they haven`t been worked before, you could get a nice surprise. Same with obvious crevices. If they are in the right position and have only been half-cleaned, do it and bar down the sides and bottom while you are at it.
Part 2
From: Roscoe Sent: 12/11/2006 8:48 AM
More of the same.
We know that heavier pieces of gold tend to find their way towards bedrock and, barring a blocking medium like thick clay layers, will do so. Likewise the denser minerals such as magnetite (black sand), tin, ilmenite, even rutile in certain districts. Certain gemstones like sapphires, garnets and zircons can show up in the null zones, too. So this gives us an indicator if we are trying to determine where gold Will be dropped in flood periods. Find the indicator mineral for that particular stream and you will know when you are working the most likely area. Of course, chasing indicators means you have to do regular cleanups or inspections to see whether you have crossed the drop zone. Rather than shut down a bigger production dredge, I prefer to power a small inspection dredge by inserting my jetter hose into a custom eductor jet, and using the suction to clean out the first few riffles on the main dredge without doing more than running clean water through the main dredge while removing the trapped concentrates. A two-man job, naturally. Having a mate monitoring the heavies keeps me on track if I hit a pay streak or indicator minerals. Shallow streams where I`m taking up all the overburden and base level gravels don`t need a constant check, but deeper deposits save time and money by letting you know when (or if) you are running hot.