PROCEEDINGS OF SECTION C. 445 



character of the enclosing matrix — firstly, as irregular inclusions in 

 the compact white quartz, usually of a symmetrical outhne or lamellar. 

 In this form it occurs isolatedly, with no associated mineral. Secondly, 

 as radial spherical crystal groupings in the rock of fine-grained texture. 

 Thirdly, as regular rhombic crystal forms in a normal matrix, usually 

 associated with tinstone. The country rock is an arenaceous mica 

 schist. The main bulk of ore is obtained by surface work upon the 

 decomposed dyke and its sheddings on the hill slope." 



The ore in this locality is a mixture of cassiterite and mangano- 

 tantalite, similar to that found at Wodgina, W.A., as shown by the fol- 

 lowing analyses taken from the report : — 



fl 2 



Tantalic oxide, TaaOs 41-70 . . 55-52 



Niobic oxide, Nb^Os 19-00 . . 24-92 



Tin oxide, SnOo 21-00 .. 4-40 



Manganese protoxide, MnO . . 14-83 .. 11-16 



Iron protoxide, FeO 2-14 . . 2-73 



Undetermined 1-33 .. 1-27 



100-00 . . 100-00 



Bynoe Harbor. — Tantalum ore occurs as dyke disseminations on a 

 mineral Hcence nine miles south of the Leviathan Tin Mine, and also 

 on Horden and Paull's claim, close to the other deposit. 



Port Darwin. — Tantalum ore is described as occurring in a similar 

 manner six miles east of King's Table, West Arm of Port Darwin. 



Western Australia — Aloolyella.— This locality, 10 miles north- 

 east of Marble Bar, is chiefly of importance for the tin ores which are 

 produced there. According to the report of Mr. A. Gibb Maitland the 

 field hes in the midst of a large area of granite, which is intrusive into 

 sedimentary rocks of probably Cambrian age. This granite is traversed 

 by numerous dykes of a pegmatite composed mainly of quartz and albite, 

 with subordinate mica, garnet, and cassiterite. Considerable quantities 

 of stream tin are being obtained in this field, this ore being undoubtedly 

 due to the disintegration of the pegmatite dykes 



In a parcel of stream tin ore in the museum of the Geological Survey 

 of Western Australia is a single fragment of a mineral forming a quad- 

 rant of a sphere lin. in diameter, with radiated crystalhne structure. 

 This mineral is of an intense black color, with a metallic lustre, and 

 specific gravity 7-3. It is identical in appearance with some of the ore 

 from Wodgina, and is without doubt manganotantalite. It is an aggre- 

 gate of a number of wedge-shaped crystals, the mass parting readily 

 along radial planes on being struck. Closely attached to its outer 

 surface are numerous small fragments of quartz and several fragments 

 of much altered albite. These indicate the original source of the mineral 

 to have been those quartz-albite pegmatite veins which form the matrix 

 of the cassiterite. 



Another similar, but smaller, fragment occurs in a second sample 

 of stream tin ore, and others still smaller may easily have been over- 

 looked. 



