[Proc. Eot. Soc. Victoria, 34 (N.S.), Pt. II., 1921]. 



Art. XV f. — -Gold Specimens from Bendigo and their 

 Probable Modes of OHgin. 



By F. L. STILLWELL, D.Sc. 



(Plate I.) 

 [Read November 10th. 1921]. 



The gold in the Bendigo quartz reefs occurs as particles of 

 bright, yellow, free gold, of high quality, containing about 30 

 parts per 1000 of silver. Its occurrence can be divided into two 

 general types — 



(a) As particles associated with the dark laminated seams 

 traversing the quartz; 



(b) as particles embedded in white quartz. 



While these two general types are not confined to any particular 

 form of reef, it can be said that the first type is more charac- 

 teristic of saddle reefs and leg reefs, and that the second type is 

 more characteristic of " spurs," which are veins cutting across the 

 strata. The gold particles in the spurs are, on an average, larger 

 than the gold particles associated with the carbonaceous seams,, 

 but the latter may be more numerous, and have formed the main 

 factor in the richest saddle reefs of Bendigo. Such particles 

 are occasionally so numerous as to form a sheet of gold along 

 the lamina.^ 



The particles of gold embedded in white quartz appear as 

 shotty specks, or as sheeted interlacings with quartz, and some- 

 times ankerite. The gold particles, like quartz, are allotriomor- 

 phic, and do not assume their crystalline form except in rare cases 

 in vugs. The tendency of the gold towards its crystalline form is, 

 however, often sufficient to produce more or less rounded, shotty 

 particles, unless there exist obstructing or modifying circum- 

 stances. The shotty particles sometimes are readily loosened 

 and detached from the quartz, and are then spoken of as " loose- 

 gold." The modifying circumstances may develop during the 

 later stages of growth of a vein if the quartz crystals grow at 

 a more rapid rate than the gold crystals, or if the growth of the- 



1. Gold Deposition In the Bendigro Goldfield. F. L. Stillwell, Bull. 4, Com- 

 monwealth Adv. Council of Sci. and Ind.. plate III., fig. 2. 



