30 T. S. Hart: The Mineralogical Cltaracter 



of other minerals, more especially those usually found near gran- 

 itic rocks. Native antimony, stibnite and jamesonite are 

 recorded from this field. A number of the rarer minerals here 

 are found in veins separate from those of the ordinary type as 

 noticed below. A remarkable variation is found near the great 

 vugh of the Eaglehawk Reef, Maldon, the quartz being replaced 

 by cacholong or common opal, in which were garnet, amphibole, 

 ferrocalcite, arsenopyrite, galena and sphalerite. 



Indication of gold by the minerals of the reef. — The associa- 

 tion of richer portions of the reefs with carbonaceous material 

 has already been noticed. With regard to the minerals of the 

 reef themselves, it is often difficult to get exact information as to 

 their bearing on the gold contents. It remains an open question 

 in many cases whether the greater richness in gold is connected 

 with the appearance of certain definite minerals or with the 

 general increasing complexity of the mixture. An increase in 

 the amount of the sulphides is usually accompanied by increased 

 gold contents. 



The appearance of sphalerite or galena in a reef of this type is 

 always regarded as an indication of probably better grade stone. 

 Opinions differ, however, as to which of these is the better, but 

 the balance is in favour of the sphalerite. I have only once 

 heard of an instance in which this mineral was not regarded 

 favourably, and, in this case, the information was not very 

 reliable or complete. It should be remembered that this mineral, 

 being the lightest of the metallic minerals in this type of ore, is 

 less readily saved by the ordinary processes, and its pale and 

 lustreless appearance when crushed renders its loss less easily 

 detected. At Maldon, according to the report already quoted 

 (10), arsenopyrite, sphalerite, and stibnite are regarded as the 

 most favourable to good gold. Pyrrhotite according to the 

 same authority is good in small quantity, but in larger quantity 

 usually bad. Ulrich (1) quotes assays from the wall of the 

 Tiverton Reef, Maldon, as giving from material containing 

 pyrrhotite, 2 to 10 oz. gold per ton. 



Arsenopyrite seems to be usually more favourable than pyrite. 

 A sample of slate from Ballarat East, without quartz, but with 

 ■crystals of arsenopyrite, gave 3 oz. to the ton, and a roughly con- 



