84 THE MINERALS OF TASMANIA. 



trict ; with complex lead-zinc sulphides, as at Mt. Read 

 and the Rosebery districts ; with silver-lead, as at the 

 Devon and other mines of like character ; and with 

 alluvial tin ore, as at various places in the north-east 

 mining districts. 



The auriferous drifts are of late Tertiary age, and some 

 of the fields have produced large quantities of the precious 

 metal, notably the Lisle field, which is reputed to have 

 produced from 10 to 15 tons of gold. The basin of the 

 King River, vicinity of the Pieman River, Long Plain, 

 Lefroy, Beaconsfield, Bell Mount, and Mathinna have each 

 produced large quantities in the past. 



The average purity of Tasmanian gold is about 96 per 

 cent., the balance being the metals of the platinoid groups. 

 The two largest nuggets obtained were discovered at the 

 Rocky River, a tributary of the Pieman, in 1883. Their 

 respective weights were 143 and 243 oz. Auriferous quartz 

 reefs have been discovered in almost all portions of the 

 island where the older Palaeozoic formations occur. The 

 strata are presumed to be the Lower Silurian (Ordovician) 

 epoch, but those of the Queen River and Middlesex dis- 

 tricts may be of Upper Silurian age. The prevailing rocks 

 are slate and sandstone, except in the Golconda district, 

 where the auriferous reefs apparently exist in the intrusive 

 granite which has pierced the sedimentary rocks of the 

 locality. 



A few peculiar features as to the paragenesis of gold and 

 other local peculiarities may be interesting and worthy of 

 record. At the Campbell's Reward Mine, near Mt. Claude, 

 a few miles below the bridge at Lorinna, the precious 

 metal occurred in a very small vein or fracture plane in a 

 rock that has been termed porphyritic syenite ; the gold 

 was faced on to the rock with a backing of decomposed 

 felspar, and occurred in fern-like arborescent patches 

 occasionally altering to radiating masses, the whole present- 

 ing a very peculiar and unique appearance. Much of the 

 separated metal had the appearance of irregularly chopped 

 hair, each fragment as seen under the microscope being 

 covered with extremely minute recurved barbs. Scattered 

 throughout the mass were also flakey plates of extreme 

 tenuity, the surface of these being covered with sub- 

 crystalline reticulated impressions. The general structure 

 of the metal and its mode of occurrence differ very much 

 from any other auriferous formation known to exist in the 

 island. The Long Plain alluvial goldfield was noted for 

 the numerous and remarkably fine crystal groups of the 



