bastin: colloidal gold and silver 71 



believes, however, that the transport of silver or gold in colloidal 

 solution is of very much less importance in downward enrich- 

 ment of ore deposits than their transfer as salts in true (electro- 

 lytic) solutions. In primary ore deposition colloidal transport 

 may be of much more importance. 



General. The writer regrets that he has been unable to carry 

 out these experiments quantitatively, determining fully the prod- 

 ucts of the reactions. He has also had no opportunity to make 

 a careful search of the foreign literature to determine how much 

 of originality can be claimed for the results. In this country, 

 however, attention appears not to have been directed to the 

 possible geologic bearing of these phenomena. As the writer 

 will be unable for some time to continue these studies the pre- 

 liminary data are offered for whatever suggestiveness they may 

 have to those interested in the role of colloids in ore deposition. 



As evidencing the occasional occurrence of gelatinous silica 

 in considerable amounts in mineral deposits, the following 

 statement by Mr. J. H. Levings^ may be of interest. 



I was surprised to find that members could only instance one case of 

 silicic acid in the gelatinous condition. About four years ago, when 

 the writer was connected with the Great Austraha Mine, Cloncurry, 

 Queensland, a drive was beat out under the siliceous copper outcrop. 

 Water was continuously flowing through this ore body, which acted 

 as a drainage conduit for the surrounding country. Numerous vughs 

 were cut into, and silica in all stages of gelatinization was found, vary- 

 ing from a viscous fluid to veins which could be cut with a knife hke 

 cheese. The writer de-hydrated many samples; some were practi- 

 cally pure silica, some contained carbonate of lime and carbonates of 

 copper. In other samples, taken from solidified portions, a complete 

 gradation from silica to calcite could be followed. Apparently, silica 

 and calcite can be precipitated from the same solution in any pro- 

 portions. It may be mentioned that the lode occurs in diorite. 



Some years previously, in Tasmania, some jelly-like substance was 

 brought for the writer to determine. It had been obtained from a 

 vugh in a siliceous copper lode, and contained some free slender quartz 

 crystals about 2 inches long, both ends of which terminated in prisms. 

 Some similar but better proportioned crystals about ^ inch long, were 

 also present. On examination the substance was found to be silica 

 in a gelatinous state. The lode occurred in old sedimentary rocks. 



8 Trans., Institution of Mining and Metallurgy, 21 : 478. 1911-1912. 



