Gippsland Auriferous Ores 



11 



It would therefore appear that, though gold is more readily 

 attacked by hot chlorine than by cold, the same is the case with 

 other materials also, and on a large scale ; so that there is a 

 positive disadvantage in charging the vats with hot ore. The 

 extractions obtained from a large number of parcels varied from 

 93 per cent, to 97"6 per cent, of the gold contents. 



Tests were always made in the laboratory on a few pounds of 

 the roasted ore, to determine the amount of chlorine to be used, 

 the time of contact to be allowed, and the extractions ; and 

 these afforded an infallible guide as to results on a larger scale, 

 with the exception of time. It was found that while 24 hours 

 might serve for a laboratory test, it took double that time to get 

 the same result from some tons of material. It was also found 

 that while the rate of dissolution went on rapidly at tirst, it 

 became slower and slower, and in course of time practically 

 ceased ; so that there is a limit to the amount of gold to be 

 extracted in a given time. 



No difficulty has been experienced up to the present in treating 

 the low-grade bullion mentioned before, although most writers 

 have judged it would be difficult to deal with by chlorination. 



When the whole of the wash liquor has been drained into the 

 precipitation vat, there is usually enough lead present in solution 

 to form a precipitate when sulphuric acid is added. Sulphate of 

 iron solution and sulphuric acid (the latter to prevent the 

 precipitation of basic sulphates) are added and stirred well; the 

 precipitate formed — gold and sulphate of lead — falls rapidly, but 

 is allowed to settle for 24 hours. The supernatant liquid is then 

 tested, to see if any gold is still in suspension, and if there is 

 none, the liquor is siphoned off, one leg of the siphon being- 

 attached to an india-rubber tube kept near the surface of the 

 liquid by means of a float, and the other discharging into a 

 mixture of sawdust and charcoal in an earthenware cylinder. 



A .solution of auric chloride is used to test the liquid draining 

 off at different levels, as it sometimes happens that the upper 

 layers may have exce.ss of sulphate of iron and the lower ones 

 still contain dissolved gold. 



When the liquor has drained to within three inches from the 

 bottom of the precipitate vat, the siphon is withdrawn, and the 

 auriferous sludge washed out with a tine jet of water into a deep 



