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All the system previously described (dredging and washing) goes installed on top of a raft, which is constituted by two boats or canoes placed parallel, and on which one installs a wooden booth in the shape of a floor. The surface of this floor is variable, depending on the length and capacity of loading of the boats (in average, a raft has an area of 8m. x 6m.).

The raft goes covered, and for its mobility in the river they are implemented with stationary motors of 36 HP, or they are towed with auxiliary canoes supplied with motors out of side of 55 HP.

Personnel
The personnel who operates a dredged unit is composed basically by three divers and the manager or owner of the raft. In the practice, the ones who control all the operation (dredging and washing) are the divers, the ones who effectuate turns of three hours in the scuba diving. The owner mainly supervises the refining process, amalgamating of gold.

For our part, according to our observations, we consider that one operation rationally taken, demands the following personnel:

• one manager (owner);
• one mechanic – motorists;
• one cook
• three divers

Operation Costs
The owners of the dredges do not take a control of their operations, factor which incorporates of not knowing of the volume of the processed material; do not allow to calculate the unit cost of their operation.

Nevertheless, referentially and in base of the information received in the land, we have proceeded to calculate the costs/month which the operation would demand of a dredge unit of 6”; having obtained monthly costs of the order of US$ 5,797.25 (annexed N° 1).

On the other hand, if we consider the technical parameters (according to bibliographies), for the income of a pump of 6”, and we could assume an average efficiency of 6 m3 per hour of gravel, it could be used for a days work of 9 hours and 25 operating days, a washing volume of 1,350 m3/month which referred to the cost/month calculated in US$ 5,797.25/month, we would get a unit cost of total $ 4.29/m3 (detail, annexed N°2).