189 



OF THE TIN ORE DEPOSITS OP MOUNT BISCHOEF, 

 TASMANIA. 



By Baron Von Groddeck, Chief Mining Councillor ot 

 the Hartz Mining Districts, and Director op the 

 Eoyal Prussian Academy oe Mines at Clausthal, 

 Germany. 

 (Translated by Edgar Wolfhagen, M.B., Hobart from the 

 Special Imprint of the "Magazine of the Geological 

 Society," 1886.*) 



By the highly interesting description which M. Schroeder 

 has givett of the topaz deposits in the Schueckenstein and its 

 surroundings, my attention was again drawn to the collection 

 of specimens of minerals from Mount Bisehoff, Tasmania, in 

 the possession of the Eoyal Academy for Mineralogy m 

 Clausthal This collection has previously afforded me an 

 ooDortonity for making a communication about a porphyrinic 

 topaz rock and about a peculiar topaz tourmaline deposit m 

 the Tasmanian tin district. 



According to M. Schroeder, the well-known topaz rock of 

 the Schueckenstein (to which I have already referred m my 

 description of the Tasmanian porphyntic topaz rock as an 

 analogous formation) appears in a narrow topaz-bearing 

 zone " which extends almost at right angles to the limit of 

 granite at the Laubach, and runs in an east-north-easterly 

 direction across the Schueckenstein to the granite ZO ne It 

 belongs to the outer zone of contact of the latter, or to its 

 immediate neighbourhood." ; 



M Schroeder has shown conclusively that witJun tins zone 

 a transformation of the quartz-porphyry and tourmaline slate 

 into topaz has taken place. He remarks that the topaz thus 

 transformed from quartz-porphyry, has a general resemblance 

 to the Tasmanian topaz-rock described by me. The calcite, 

 however, contained in the Tasmanian specimens is absent in 

 the former, but it contains a certain amount of tourmaime. 

 This difference in the accessory constituents does not seem 

 to me to be of any great importance. , 



On account of the structure of the porphyria topaz rock 

 described by me, which exactly resembles that of quaitli- 



any rate, from Australia ; very minute P^hculai a* ^^ libel, "Mount 

 are, for obvious reasons, not attached to them »™M^j£tah and Penguin 

 ^^LS^^A^^to^^^^ of its rich mineral 

 deposits. 



