376 Notices of Memoirs — Tungsten Deposits of Essexvale. 



most promising reefs exposed are respectively about a mile long and 

 half a mile long so far as proved. These are the Rhoda reef in the 

 north-eastern portion of Plot 27, and the reef running through the 

 Lunar and Moon blocks near the common boundary of Plots 37 and 38. 

 With one exception the reefs examined strike east to west and dip 

 north at angles varying between 30° and 55°. The reef on Plot 4 

 strikes north-west to south-east and dips north-east at 53°. 



The width of the reefs is of course variable owing to the lenses of 

 quartz. Apart from the quartz lenses, the width averages three feet, 

 and is surprisingly constant. 



In each instance the country is coarse massive hornblende granite 

 without signs of shearing or faulting between the reef and the 

 country. It appears, therefore, that the aplite was injected along 

 master joint planes caused by the contraction of the granite on 

 consolidating, and not in fissures caused by faulting. This may have 

 an important bearing on the persistence of the greisen bodies below 

 the surface. In a few instances the mica greisen has a slightly 

 schistose appearance. In a few places greisenization of the country 

 is suspected, but this is on a small scale only, and no tungsten ore 

 has been discovered in it. 



With the exception of the Union Jack reef in the north-west corner 

 of Essexvale Reserve the aplite has been completely greisenized so 

 far as can be judged by the small amount of reef exposed. At the 

 Union Jack the intrusion exceeds six feet in width, but about a third 

 of it consists of white aplite apparently ungreisenized. 



Stockworlc Deposit. — The block upon which most work has been 

 done differs from the above blocks, which maybe taken to be normal. 

 The occurrence in question is situated on Tungsten Kopje, a prominent 

 hill of massive hornblende granite with a low ridge extending about 

 300 yards to the east and a longer one to the west. 



The fact that a large amount of float wolframite occurred 

 immediately around the hill led to prospecting on the hill, with the 

 result that a stock work deposit was discovered extending along the 

 eastern and western ridges and on the north flank of the hill. 



Throughout the massive hornblende granite of this zone streaks 

 and seams of aplite containing gashes of quartz are scattered rather 

 sparsely and quite indiscriminately. These seams run in all directions 

 and at all angles, many are nearly flat, but some are vertical ; they 

 make small saddles in several places, but pursue irregular courses, and 

 expand and die out quite irregularly. They average a few inches wide 

 and in no instance exceed a foot. None are traceable for more than 

 a few yards. The greisen always carries streaks of quartz and occurs 

 on one or both sides of the latter. The aplite varies in degree of 

 greisenization. In some parts the greisen consists of sugary quartz 

 and pyrite with very fine wolframite scattered through it but invisible 

 to the naked eye. Such a rock weathers brown and strongly 

 resembles sandstone. It is always present in the rotary concentrate. 

 In other parts the greisen consists chiefly of a soft yellow mica. 



At the south-west end of this deposit a body of greisen about 

 6 feet wide, striking north to south and dipping about 40° E., has 

 been opened and afforded rich patches of wolframite. 



