298 PEOCEEDIKGS OF THE GEOLOGICAL SOCLETY. [April 24, 



ditions that should lead to such a result by after-reduction of the 

 silver salt. 



A specimen from the "Last Chance" reef in the New-Zealand 

 Gully, near Rockhampton, shows specks of metallic gold dissemi- 

 nated through a mass of chloride of silver. It has not yet been 

 examined to see if any portion of gold may be in a form soluble in 

 hj'posulphite of soda. 



Prom 7 tons of the vein- stuff of the " Last Chance" 240 ounces 

 of gold were washed. The harder portion, which would not " puddle 

 down " when crushed and amalgamated, yielded a bar of metal very 

 pale in colour, and with a much higher percentage of silver than the 

 washed-out gold from the same reef. 



This was due to the abundance of " poison-stone," as the owners 

 called the horn silver, which remained among the harder portion of 

 the reef sent to the stampers. 



Though this and other cases of a similar bearing would suggest 

 that both gold and silver were originally in solution as chlorides (the 

 latter by the solvent power of an alkaline chloride) , yet the difficulty 

 of precipitating the two metals together from such a solution has yet 

 to be overcome. The more constant association of native gold with 

 pyrites would also draw our attention in another direction. 



A series of experiments now in hand may throw some light on this 

 complicated question ; and when completed they will form the ma- 

 terial for a further communication to this Society. 



Whatever may have been the solvent and precipitant of the nobler 

 metals in the auriferous vein-stones associated with trap-intrusions, 

 all other but hydrothermal action may safely be eliminated, the very 

 nature of the reefs, composed as they are of alternating layers or of 

 a promiscuous mixture of quartz, calc-spar, pyrites, &c., affording 

 unmistakable evidence on this point. The gold also contained in 

 the trap-dykes themselves is always accompanied by pyrites — both, 

 in my opinion, hydrothermal products separating out diiring the 

 cooling down of the trap-intrusions. 



Auriferous lodes, occurring in areas where hydrothermal action 

 has attended trap-disturbances of a special character in Queensland, 

 are generally thin — to be estimated by inches rather than by feet ; 

 but, taken as a whole, they are far richer in gold than those enclosed 

 by sedimentary rocks. 



The yield of the principal Gympie reefs for the year 1869 was 

 11,996 tons of quartz for 76,870 ounces of gold, being an average of 

 6 ounces, 8 dwts., 4 grains per tou, the highest return of perhaps 

 any gold-field in the world. The cost of mining such reefs, how- 

 ever, is much greater than where the vein-stones are better defined 

 and of a good average thickness throughout. 



The following Table, showing the thickness and yield of most of 

 the reefs in the Rockhampton district, affords a fair representation 

 of the character, thickness, and general conditions of the auriferous 

 lodes found in the other mining- districts included within Palseozoic 



