446 PROCEEDINGS OF SECTION C. 



Cooglegong.— This tinfield occurs 30 miles to the south-west of 

 Marble Bar. According to the researches of Mr. A. Gibb Maitland, 

 it is situated in the midst of a large area of granite, which, in places, is 

 gneissic. " The granite is intersected in certain localities by veins of 

 pegmatite, which have doubtless been the original source from which 

 the stream and residual tin have been derived." 



Gadolinite has been found b ith in the stream deposits and, asso- 

 ciated with cassiterite and monazite, in a pegmatite vein. 



In a paper on this occurrence of gadolinite, read before the Royal 

 Society of New South Wales, in October, 1902, Mr. B. F. Davis says : 

 — " Amongst the minerals I brought from the north-west I have two 

 varieties of a mineral allied to ' euxenite ' in physical characteristics, 

 as described by Dana. One differs from the other in having more 

 manganese in the place of uranium. They are essentially niobates 

 and titanates (with tantalum) of uranium iron and yttrium earths, with 

 cerium earths and thorium. They occur with cassiterite and monazite 

 in the washdirt. I have only a few small pieces, but one mineral at 

 least was not uncommon. I saw it in all the tin ore bagged from 

 different parts of the country." 



Some of the mineral from this same locality, collected from samples 

 of tin concentrates by Dr. McKenzie, of the Tin Smelting Works, 

 Sydney, has been examined by Mr. D. Mawson, and found to be strongly 

 xadio-active. 



It is not, however, at all clear from Mr. Davis's paper whether this 

 mineral was really obtained at Cooglegong or not. It may possibly 

 have come from Moolyella. 



I have recently come across some specimens in the West Australian 

 Museum, the locality of which is given as the Shaw River, so that they 

 come either from Cooglegong or from the Old Shaw Tinfield a few miles 

 out of Cooglegong. These specimens consist of a number of angular 

 detrital fragments of typical euxenite, varying in size from 10 to 40 mm. 

 in length, and coated externally with a brown clay. On a fresh frac- 

 ture the mineral is brown in color, and possesses a brilliant resinous 

 lustre. It has a specific gravity of 5-3. 



Thelemanri' s Find. — Sixteen miles north-west of Lalla Rookh 

 tantalum ore was obtained in 1906 by Mr. F. Thelemann. It is de- 

 trital ore, and is said to occur only in limited quantities. It is of little 

 commercial value, being a low-grade iron columbite. assaying from 

 3 per cent, to 5- per cent, of tantalic oxide. One sample, consisting of 

 more or less worn fragments from ^in. to lin. in diameter, contained 

 4-92 per cent, of tantalic oxide, 70-34 per cent, of niobic oxide, and no 

 tin. The specific gravity of the constituent fragments was very uniform, 

 averaging 5-5. 



The ore from this locality is frequently well crystallised. One 

 good crystal measuring 7mm. x 23mm. x 30mm., and having a specific 

 gravity of 5-53, shows the following faces : — a, 100 ; b, 010 ; c, 001 ; 

 u, 133; e, 021; m, 110; g, 130; y, 210. The lower half of this 

 crystal has not developed, having apparently formed against an already 

 crystaUised mass of albite. Several other crystals, with fewer faces. 



