Saturday, July 12, 2008

"Reading" a Stream: Drywashes



In earlier posts on the subject I covered some of the basics of placer gold deposition as it relates to stream courses with continual water flow. Drywashes can, however, pose a different set of problems for the small-scale miner.

Intermittent Flow Means Intermittent Gold

In drywashes or other stream courses with only occasional or intermittent water flow the basics of gold deposition and stream hydraulics still apply to some degree, but at the same time these stream "reading" factors can become quite problematic or downright frustrating to prospective placer miners. Why is this? The answer is, in essence, quite simple and direct.

In arid or desert placers where water flow is essentially restricted to sudden thunderstorm downpours, brief seasonal flooding, or other intermittent events, the bulk of the stream course's placer gold is in a transitional state. Granted, significant amounts of gold may still be found on bedrock, behind larger obstructions, or in low pressure portions of the streambed but in a drywash there is nearly the same likelihood that pockets or paystreaks of gold will be scattered throughout the stream course at various points, levels, and depths that seem to defy conventional logic governing gold deposition in running streams.

Think Outside the Box 

For example, in areas that only receive rain during sudden torrrential downpours from thunderstorms in the summertime, drywashes acting as drainages for higher elevations are usually in a flash flood state, with tons of rock, gravel, and other debris being swept downstream with great force and speed. This includes placer gold. When, just as suddenly, this flash flooding stops, the placer gold that was in suspension just seconds earlier is deposited wherever it is "dumped" at the moment stream hydraulic action ceases.

So, placer gold in drywashes can frequently be found in erratic pockets and paystreaks that often do not conform to the physics of gold deposition in a running stream with consistent hydraulic action. This creates a new set of problems for any miner attempting to "read" a drywash. Often, drywashes pose a "hit-or-miss" type of placer mining that can either be immensely rewarding or just as frustrating. When it comes to gold deposition in dry placers, thinking outside the box is a definite asset.

(c)  Jim Rocha (J.R.)  2008

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