Getting Gold: A Gold-Mining Handbook for Practical Men

by J. C. F. Johnson

The blanket table is, however, a very unsatisfactory concentrator at best, and is giving place to mechanical concentrators of various descriptions.

I have a device at present unpatented which will do away with the necessity for blanket tables or copper plates, as by the expenditure of from ½ to 1 h.-p. every particle of free gold after leaving the boxes must come within the embrace of a mercury amalgam. No cleaning of plates is required.

An ancient Egyptian gold washing table is shown in [Fig. 22]. It is a representation of an old stone table such as is referred to in [p. 2], which was used by the Egyptians in treating the gold ores of Lower Egypt. The ore was first ground, it is likely by means of some description of stone arrastra, and then passed over the sloping table with water, the gold being retained in the riffles. In these the material would probably be mechanically agitated. Although for its era ingenious it will be plain to practical men that if the gold were fine the process would be very ineffective. Possibly, but of this I have no evidence, mercury was used to retain the gold in the riffles, for, as previously stated, this method was known to the ancients.

Fig 22. Washing Table of Stone with Riffles.

At a mine at which I was managing director the lode was almost entirely composed of sulphide of iron, carbonate of lime or calcspar, with a little silica. In this case it was found best to crush without mercury, then run the pulp into pans, where it was concentrated. The concentrates were calcined in a common reverberatory furnace, and afterwards amalgamated with mercury in a special pan; the results were very satisfactory; but it does not follow that this process would be the most suitable for a slightly different lode stuff.

I was lately consulted with respect to the treatment of a pyritic ore in a very promising mine, but could not recommend the above treatment, because though the pyrites in the gangue was similar, the bulk of the lode consisted of silica, consequently there would be a great waste of power in triturating the whole of the stuff to what, with regard to much of it, would be an unnecessary degree of fineness. I am of opinion that in cases such as this, where it is not intended to adopt the chlorination or cyanogen process, it will be found most economical to crush to a coarse gauge, concentrate, calcine the concentrates, and finally amalgamate in some suitable amalgamator.

Probably for this mode of treatment Krom rolls would be found more effective reducing agents than stampers, as with them the bulk of the ore can be broken to any required gauge and there would consequently be less loss in “slimes.”

The great art in effective battery work is to crush your stuff to the required fineness only, and then to provide that each particle is brought into contact with the mercury either in box, trough plate, or pan. To do this the flow of water must be carefully regulated; it should not carry the stuff off too quickly nor allow the troughs and plates to be choked. In cold weather the water may be warmed by passing the feed-pipe through a tank into which the steam from the engine exhausts, and this will be found to keep the mercury bright and lively. But be careful no engine oil or grease mingles with the water, as grease on the copper tables will absolutely prevent amalgamation.