Sometimes special difficulties crop up in the process of separating the gold from the amalgam.  At the first “cleaning up” on the Frasers Mine at Southern Cross, West Australia, great consternation was excited by the appearance of the retorted gold, which, as an old miner graphically put it, was “as black as the hind leg of a crow,” and utterly unfit for smelting, owing to the presence of base metals.  Some time after this I was largely interested in the Blackborne mine in the same district when a similar trouble arose.  This I succeeded in surmounting, but a still more serious one was too much for me—­i.e., the absence of payable gold in the stone.  I give here an extract from the Australian Mining Standard, of December 9th, 1893, with reference to the mode of cleaning the amalgam which I adopted.

New method of separating gold from impure amalgam.

I had submitted to me lately a sample of amalgam from a mine in West Australia which amalgam had proved a complete puzzle to the manager and amalgamator.  The Mint returns showed a very large proportion of impurity, even in the smelted gold.  When retorted only, the Mint authorities refused to take it after they had treated two cakes, one of 119 oz., which yielded only 35 oz. 5 dwt. standard gold, and one of 140 oz., which gave 41 oz. 10 dwt.  The gold smelted on the mine was nearly as bad proportionately.  Thus, 128 oz. smelted down at the Mint to 87 oz. 8 dwt. and 109 oz. to 55 oz. 10 dwt.  The impurity was principally iron, a most unusual thing in my experience, and was due to two causes revealed by assay of the ore and analysis of the mine water, viz., an excess of arsenate of iron in the stone, and the presence in large proportions of mineral salts, principally chloride of Calcium CaCl., sodium NaCl, and magnesium MgCl2, in the mine water used in the battery.  The exact analysis of the water was as follows:—­

     Carbonate of Iron FeCO3 2.76 grains per gallon
     Carbonate of Calcium CaCO3 7.61 grains per gallon
     Sulphate of Calcium CaSO4 81.71 grains per gallon
     Chloride of Calcium CaCl2 2797.84 grains per gallon
     Chloride of Magnesium MgCl2 610.13 grains per gallon
     Chloride of Sodium or
     Common Salt NaCl 5072.65 grains per gallon

     Total solid matter 8572.70 = 19.5 oz. to the gallon.

It will be seen, then, that this water is nearly four times more salt that that of the sea.  The effect of using a water of this character, as I have previously found, is to cause the amalgamation of considerable quantities of iron with the gold as in this case.

I received 10 oz. of amalgam, and having found what constituted its impurities proceeded to experiment as to its treatment.  When retorted on the mine it was turned out in a black cake so impure as almost to make it impossible to smelt properly.  I found the same result on first retorting, and after a number of experiments which need not be recapitulated though some were fairly effective, I hit on the following method, which was found to be most successful and will probably be so found in other localities where similarly unfavourable conditions prevail.