Methods of Gold Explorations

      The majority of large placer deposits are in South America, Africa or Asia. When one operates in a foreign, remote area, it is essential to use reliable methods, local labor, and tested equipment. Photogeology, at the initial stage, offers a 2D (surface) definition of the area and its geology. Seismic adds a 3rd dimension to lead the sampling program. It provides cross-sections of alluvial terraces with little error. The sampling in strategically selected areas gives tests on economic reliability of the deposit.                                                                                                                                                

      Here are some sampling reliable methods:

Bucket or Clamshell Type Excavators: 

    These machines are usually quite large in size and allow taking a fairly large bulk sample. The advantages of using this equipment are its ability to allow visual inspection of bedrock, use of caissons to hold the hole open, and the capability of obtaining a fairly accurate sample volume. The disadvantages are the need for good access for the large equipment and a fairly slow digging speed.

Churn Drills: 

Churn drilling is used in deep or wet ground where sampling by pits, trenches, or shafts is not feasible. The churn drill utilizes a heavy casing with a drive shoe at the bottom, a chisel-shaped bit, and a vacuum type sand pump for removing the sample from the hole. There are three main types of churn drills that are differentiated by their size: 

The hand operated "Banka", the light "Hillman" or "Airplane, "the heavy "Bucyrus-Erie" or "Keystone" drills. The advantages of using churn drills for sampling placer deposits are: (1) the sample is very reliable; (2) equipment is fairly portable; (3) few mechanical problems are encountered; and (4) technical data and interpretative information are available. The disadvantages of using churn drills are (1) very slow penetration rate, (2) large boulders create many problems,

 Special Problems Associated with Placer Sampling: These are (1) large rocks and b oulders, (2) erratic high values, (3) uncased holes, (4) small diameter holes, and (5) salting.

Large Rocks and Boulders: 

     In sampling placers, there is a tendency to bypass areas containing many boulders or to sample the easily collected finer material around the boulders. In many cases, this is essentially salting the sample since the valuable material in a placer deposit usually occurs in the finer material. The most direct solution to sampling areas containing boulders would be to take samples large enough to contain a representative portion of the boulders to give accurate value estimates. Since it is not physically possible to take large samples to include the boulders in most sampling situations, how does one consider the effect of boulders without including them in the sample? The most common solution is to visually estimate the volume and insert a correction factor into the end sample volume calculations.