452 DALE— CAMBRIAN MANGANESE DEPOSITS OF [April 25, 



ganese groundmass showing possibly a diagenetic replacement. 

 Barite also occurs as disseminated anhedral crystal grains or blades 

 in the cores and outer zones of nodules at Manuels, which is very 

 suggestive of diagenetic processes (Fig. 16, Slide 288). At Topsail 

 (Fig. 31, Slide 269) barite occurs as bundles of blades or sheath- 

 like aggregates in a manganese oxide groundmass strongly suggest- 

 ing replacement. 



In other parts of the world barium is often found replacing man- 

 ganese in psilomelane and sometimes enters largely into the com- 

 position of wad, specimens from Romaneche containing as much as 

 16.2 per cent, of BaO (Dana, 3 : 258). A very striking phenomenon 

 shown by the barite is its replacement by chlorite (Fig. 12, Slide 

 296, and Fig. 34, Slide 272). 



Just why there is this common association of two very unlike 

 elements we have no definite information. De Launay (4: 52) 

 gives the following explanation for epigenetic deposits : 



" The association between barite and manganese though very frequently 

 exhibited in surface formations, in many cases these two substances are being 

 concentrated by circulating waters in pockets or fissures of terranes." 



Various conditions may produce barite with barium salts in 

 solution but only one seems to apply to the occurrences under con- 

 sideration. As there are evidences of diagenetically and epigenetic- 

 -'lly formed barite in the deposits, it is quite possible that there has 

 been an intermingling of solutions carrying barium carbonate and 

 some sulphate resulting in the formation of barite. According to 

 De Launay (4: 52) 



" Barite being remarkably insoluble is one of those barium compounds 

 which not only has the propensity to segregate and all at once to be trans- 

 formed into the carbonate but also the tendency under the influence of H2SO4 

 produced by the superficial oxidation of the metallic sulphides to pass into 

 the state of barite." 



The replacement of the colorless barite by the pale green chlorite 

 begins about the edges and along cleavage cracks of the former. 

 The chlorite gradually spreads while the intervening portions of 

 barite decrease until wholly eliminated, resulting in a pseudomorph 

 of chlorite after barite. In general appearance of its various stages. 



