200 R. H. Rastall — The Genesis of Tungsten Ores. 



part of the colony, from the Herberton tin-field, from the Etheridge 

 mineral field, from Mount Carbine, Bamford, and other areas. In the 

 Herberton district the country rock consists of highly metamorphosed 

 sediments, including quartzite, greywacke, and shales, intruded by 

 biotite and hornblende granite, quartz porphyry, and felsite. Lodes 

 occur in all of these, containing a considerable variety of minerals, 

 including cassiterite, wolframite, bismuthine, antimonite, chalco- 

 pj'rite, galena, magnetite, tourmaline, topaz, and fluorspar. In tlie 

 Hodgkinson field wolframite and molybdenite occur in quartz veins 

 in a grey biotite granite. At Mount Carbine slates and schists are 

 penetrated by batholiths of porphyritic biotite-granite. In connexion 

 with this are pegmatite dykes and interlacing veins forming lodes up 

 to 6 feet wide. The pegmatites consist of quartz-felspar rock with 

 tourmaline, some muscovite, and a little beryl. The metallic minerals 

 are cassiterite, wolframite, arsenopyrite, and molybdenite. The 

 Avolframite appears to be more closely connected with the felspar 

 than with the quartz. One block of wolframite was found weighing 

 6 tons. There is also some scheelite. 



In the Bamford district the rocks are mainly igneous, both volcanic 

 and intrusive. Wolframite occurs as an original constituent in 

 biotite-granite, and also in. pegmatites and greisens in connexion 

 with the granite. A large number of minerals has been observed 

 here ; the chief are : wolframite, bismuth (both native and as sulphides, 

 carbonates, and oxides), molybdenite, pyrite, chalcopyrite, blende, 

 and galena; cassiterite has been found, but it is not very common. 

 Of much interest also are ilsemannite, stolzite, and the new mineral 

 chillagite, previously mentioned as an isomorphous mixture of lead 

 tungstate and lead molybdate. The ore-deposits are mainly in the 

 form of pipes of white quartz, with wolframite and molybdenite; 

 vugs are seen up to 20 feet in diameter, containing bismuth, fluorite, 

 and some sulphides; the smaller vugs are rich in wolfram, while the 

 larger ones are poor. These vugs are possibly due to stoping along 

 fissures. Although the form of the wolfram pipes is somewhat 

 unusual, they do not differ in any essential feature from the common 

 type of wolfram-molybdenite pegmatites formed by solidification of 

 the last residues of a granitic magma in which these elements have 

 been segregated by differentiation or concentration, whichever word 

 is preferred in this connexion. 



From the published descriptions of the Queensland mines it appears 

 that a large proportion of the present output comes from shoad 

 deposits, which are locally described as alluvial*. This material does 

 not appear, however, as a rule to have been transported for any 

 distance, but rather to be a true residual deposit. 



Wolframite is also found in the tin area of Mount Bischoff in 

 Tasmania. Here quartz-porphyry dykes, intruded into Palaeozoic 

 sediments, have undergone intense pneumatolytic metamorphism, 

 being largely replaced by secondary minerals, including cassiterite, 

 wolframite, arsenopyrite, pyrrhotite, tourmaline, topaz, and fluorite. 

 Perhaps the most striking feature here is the great development of 

 topaz in the altered dykes. 



The extraordinarily rich lodes of the provinces of Oruro and Potosi 



