332 Revieivs — Geology of Ainsivorth Mining Camp, E.G. 



sL owing all variations from pure quartz to pure felspar. The quartz- 

 rich pegmatites predominate in the granite and the felspar-rich 

 in the granophyre. The minerals of the rare earths are entirely 

 absent from the pegmatites of this portion of the Bushveld complex. 



There is a short note on the local occurrences of norite and 

 pyroxenite, and the lithology of the various sediments of the Water- 

 berg system in the area is dealt with in detail. A short account is 

 given of the volcanic series* which appears originally to have con- 

 sisted chiefly of hyalopilitic andesites : these have suffered intense 

 secondary silicification, a phenomenon not exhibited by the tufis 

 and sedimentary rocks with which the lavas are interbedded. 

 Quartzites and shales of the Pretoria series are overthrust on to 

 the Waterberg system in the southern part of the district. Quartz 

 veins, traversing the central portion of the area, show many 

 structures and variations — one, 150 yards wide, has induced intense 

 sericitization in the adjoining granite and granophyre up to 200 yards 

 on each side. 



Turning to economic geology, the chief mineral deposits of the 

 area are cassiterite, scheelite, copper ore, and white arsenic. The 

 ore deposits are very erratic and consequently difficult and expensive 

 to work. An account of the fifty minerals identified is given, and 

 an analysis is shown of the " raven-mica " which, as at St. Just and 

 Altenberg, accompanies the cassiterite (in the granophyre). 

 Cassiterite is the only recoverable mineral in the granite, and was 

 apparently formed before the main period of sericitization. The 

 normal granophyre never forms the country rock for mineral deposits, 

 all deposits being in syenitic modifications of, or pegmatitic bodies in, 

 the granophyre. The individual deposits in these rocks are 

 described in detail, as are those in the Waterberg quartzite. All the 

 deposits are evidently genetically connected with the Bushveld 

 granite, and the author distingaishes five phases of deposition- 

 With regard to the vehicle of deposition, no satisfactory conclusion 

 is reached, though it is of interest that no tourmaline has been found 

 except in one pipe. 



The memoir finishes with chapters on the Mining and Ore Treat- 

 ment, and the Future of the Fields. 



J. E. A. W. 



Geology and Ore Deposits of Ainsworth Mining Camp, British: 

 Columbia. By S. J. Schofield. Memoir 117, Geological 

 Survey of Canada. pp. iv + 73, 12 maps and diagrams,. 

 3 plates, 6 figures. 1920. 

 ^FHE Ainsworth mining district lies in the Selkirk Mountains, 

 -*- some 400 miles east of Vancouver, just north of the Inter- 

 national Boundary. 



The sediments of the area are divided into two main groups— the 

 unfossiliferous Ainsworth series, which is pre-Carboniferous, and the 

 Slocan series, which is probably Pennsylvanian. The former consists 



