Exploration and Evaluation Methods to find gold in Alluvial deposits I

In Rio Suerte, we also care about making an exploration and evaluation of alluvial gold deposits prior to starting work squarely in the mining and gold panning Motagua River.

Here are some methods of exploration of alluvial gold that can be used.


One of the most difficult task associated with placer mining is the evaluation of the deposit. More placer projects have failed due to inaccurate assessment of reserves than any other reason. Within the realm of alluvial deposits, those containing valuable minerals with a high value unit (diamonds) are more difficult to prove than those with a larger volume of minerals of lower unit value (tin). But let’s focus on gold.

gold-pan-w.gravelSome items to consider when testing an alluvial deposit:

1) You need a relatively large sample size for accurate assessment. The alluvial deposits are composed of many sizes of gravel. This makes it difficult to obtain a representative sample.
2) When testing for mineral deposits of high unit value, such as gold, any error in the mineral content in the sample is magnified in the calculation of reserves.
3) Values ​​are erratically normally distributed within the mass of gravel. Consequently, some deposits can be evaluated with a more uniform distribution of value properly with a minimum number of samples, while a deposit with high erratic distribution of values ​​can not be adequately tested regardless of how many samples are taken.
4) The investigation of an alluvial deposit must be under the direction of a person experienced in the art of placer sampling.
5) During a program, items that must be observed and noted in addition to the sample size and the value of ore must include boulder size and number, volume of clay, bedrock conditions, water, frozen ground, false bedrock, and any other physical characteristics that affect mining the deposit.

The test programtesting

The steps to be followed for a test program:


(1) The status of the land
(2) Physical characteristics Area
(3) The investigation of the area’s mining history

Field inspection:

(1) photogeomorphology
(2) Samples of all exposures over gravel,
(3) Something seismic sections,
(4) The study geobotanical
(5) The study of old workings.

Choosing a testing method

CRAWLER_EXCAVATOR_E305CThe main methods to consider are (1) existing exposures, (2) hand-dug holes, (3) open pits backhoe, (4) open pits excavator, (5) other machine-dug holes , (6) churn drill holes, (7) other drilling methods, or (8) volume samples.

The special problems associated with placer evaluation:

These are: (1) large stones, (2) high outliers, (3) the uncased holes, (4) the small diameter holes, and (5) salted.

The processing or sample concentration:

The consideration is whether the sample should be manual or computer.

The data processing

The data processing is to keep a record of values​​, and assay procedures.

The estimation of reserves and valuation placer:

Methods that can be used for reserve estimation and valuation are:testgold

(1) the method of block
(2) the triangle method
(3) the polygonal method
(4) the method section
(5) the method of diamonds


Test methods previously profiled samples vary from simple gravel surface (exposures) to drill sophisticated methods. The arrangement and density tests should be adapted to each placer. The rule is: “A minimum of samples for a maximum of information.” In this section, various methods are discussed briefly and indicates the relevance of each:

The gravel outcrops

If gravel outcrops are available, they can be tested for potentially valuable minerals or hitting taking a sample. The advantages of taking samples from outcrops are low cost and speed that samples can be taken. The disadvantages are that you may prove what is on the surface and no quantitative information can be conceived of these samples.

Excavations Manual

These can be the pits, trenches, or shafts excavated on dry land and shallow. This test method is not used today because of the high cost of labor but can be used effectively in remote parts of the world where skilled workers are not available, or that the overall cost of labor is relatively low. The method provides a good sample size and is used often to verify the results of a sediment sinking drill a hole above the hole. Also rock above values ​​can be accurately determined when excavations are sunk to bedrock. The disadvantages are the difficulties encountered in deep earth and water saturated.

backhoe3_outlineThe backhoe trenches

The backhoes are very versatile for testing equipment relatively shallow, to about 6-m. (20-ft) deep. The backhoes are mobile, fast land can dig pretty hard, and are inexpensive compared to manual excavation. Once a trench is opened, the channel is sampled by hand or using the backhoe or a sample volume can be done with all the material from the excavation. To test programs with the backhoe, the soil should be fairly dry and stable. Care should be taken when using a backhoe, or any mechanical equipment, to maintain all fuel and lubricant away from the sample material. Contamination of the sample may cause the float fine gold and reduce the value of the sample.

The trenches of the leveler

The bulldozers are better to work on dry land, where the trenches are stable excavated 3 m (10 ft) deep or less. The greatest advantage of the survey with a large excavator trench is that the trenches allow good visual inspection of the land. Other advantages and disadvantages are similar to those of the backhoe trenches.

Other excavations dug with machines

Also the dregs or holes are dug in stable earth, using power equipment such as large augers, drilling large diameter, excavators type or “clamshell”. The wells dug with the help of power equipment and experienced operators require access convenient machine.


Auger, for trying alluvial deposit, may vary depending on size of machines;’s small hand held machines classify large truck-mounted. The augers are relatively inexpensive to operate and can provide large sample volume. The disadvantages of using augers are its inability to penetrate soil with stones, gold classification can occur with bits of spiral type, and their inability to make samples in waterlogged soil.

Excavators large type or “clamshell”:

These machines are usually quite large and allow taking a large sample volume. The advantages of using this equipment is its ability to allow use of drawers to hold the hole open for visual inspection of the bedrock, and the ability to obtain an accurate sample volume. The disadvantages are the need for good access for the large excavating equipment and a rather slow speed.

Rotary drills:Rotary 450 Portable drill rod

The rotary drill is used in deep water or saturated where testing holes, trenches or shafts is not feasible. The rotary drill uses a heavy tube with a crown at the back, a head of chisel-shaped drill, sand and a vacuum pump for removing the sample from the hole. There are three main types of rotary drills that are differentiated by size:
the manual “Banka”
the light “Hillman” or “Airplane”
the heavy “Bucyrus-Erie” or “Keystone”.

The advantages of using rotary drilling, to test placer deposits are:

(1) the sample is very reliable;
(2) the equipment is portable;
(3) are few mechanical problems;
(4) the technical and interpretive information are available.

The disadvantages of using drills classmate are:

(1) the proportion of very slow penetration,
(2) large boulders create many problems.

Some of the special problems associated with testing placer

Large stonesGranite boulders and reflections on Tidal River

During testing of the alluvial deposits, there is a tendency to bypass areas containing many large stones and easily test the finer material gathered around the boulders. In many cases, this is essentially salting the sample from which the valuable material in an alluvial deposit normally occurs in the finer material. The most direct solution to test areas containing large stones would take samples large enough to contain a representative portion of the large stones to give accurate value estimates. Since you can not physically take large samples to include large stones in most situations, how to consider the effect of large stones without including them in the sample? The most common solution is to estimate the volume visually and insert a correction factor in the calculations of the last volume of sample.

Erratic high values

The methods used to estimate the value of placer ground rely on the assumption that the value found in a particular sample extends halfway to the next sample. While the assessment of the land which has a generally low or even average values ​​can be done using methods standard reserve estimation, the high outlier test deposit cause problems. Methods for adjusting high outliers, so an over land does not occur, include: (1) resampling erratic areas, (2 determined using the lowest value, (3) to determine what should be the fair value plus high and then save the values ​​of all samples within that limit.

Embedded non Holes

Using non embedded drill should be discouraged in alluvial deposits tests, especially with a high mineral unit par value. If using embedded odd holes, there is a tendency to unintentionally salar sample and sample results overvalued. This problem arises due to the fact that without the cover, excess material can enter a sample without the evaluator knows where, into the hole, the material came. An exception to the use of embedded drills when drilling is the frozen earth. If the soil is very cold test, the cover is normally not used. That in the Rio Motagua no problem.

The small diameter holes

Due to the large “nugget effect” associated with evidence of land containing valuable minerals unit pair, the use of small diameter drill testing is not recommended for deposits of gold, platinum or diamonds, etc.. When testing deposits that have fine grains of material, or have low value pair mineral unit, the small diameter bore 50 mm (2-in.) Can be used.

The Salting

Salting of samples can occur intentionally or unintentionally. The salting is the intentional deliberate addition of a valuable mineral sample. The salting unintentional or innocent is usually the result of sloppy testing procedures or improper. No matter how salting occurs, the results can mean the failure of a project after many thousands or even millions of dollars spent to bring a property into production. (TO BE CONTINUED…)

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