30 0. A. Derby — Manganese Ore Deposits 



It results from the above observations that' the ore bodies of 

 the Queluz district are residual deposits derived through decom- 

 position and leaching from an original type, or types, of rock 

 in which manganese garnet was the most constant and charac- 

 teristic silicate element. With this, which often constituted 

 almost the entire bulk of the rock, were associated minerals of 

 the amphibole (and perhaps pyroxene) or mica series, and in 

 some phases free manganese oxide that when in predominant 

 proportions gave a type corresponding to that of the free iron 

 oxide (magnetite) and manganese garnet rock of the Barbacena 

 district, or, in more general terms, to the well known types of 

 magnetic or titaniferous iron oxides with various silicates. 

 The occurrence of garnetiferous quartzites appears to indicate 

 that in some cases quartz may also have been a primary consti- 

 tuent, though for the most part it seems to have been of second- 

 ary origin. As accessory elements, ilmenite and rutile are 

 of frequent though not of constant occurrence, while apatite, 

 though positively recognized in two specimens only, appears 

 to have been constant since a small proportion of phosphorus has. 

 been found in all analyses in which it was looked for. A 

 remarkable feature, considering the highly basic character 

 above deduced for this type, is the absence, except sporadi- 

 cally as ilmenite, of free iron oxide and the low proportion of 

 combined iron as shown by the analyses of the residual ores in 

 which a concentration of this element is presumable. The 

 Barbacena ore, however, shows that, exceptionally, free iron 

 oxide may occur and even rise to a predominant proportion. 

 Another remarkable feature is the tolerably constant, though 

 sporadic, appearance of graphite, though as will be shown 

 below this is probably an introduced element. 



This type, which may appropriately be denominated queluzite, 

 is more or less intimately associated at Sao Goncalo, Morro da 

 Mina and Barroso with decomposed schistose rocks that evi- 

 dently contained an original manganese-bearing silicate and 

 which from the absence of recognizable clastic elements and 

 from other characteristics, so far as they can be made out, is 

 presumed to have been an amphibolic schist representing a 

 sheared basic eruptive. At Agua Limpa a confirmation of this 

 deduction is afforded through the presence in almost immedi- 

 ate contact with the ore body of a feldspathic amphibole schist 

 containing manganese garnet, which is almost certainly a 

 sheared eruptive and, although its original character cannot 

 be positively determined, probably of dioritic, gabbroitic or 

 noritic character. At Morro da Mina, Sao Goncalo and Agua 

 Limpa there is also in close connection with the ore an 

 unsheared eruptive (represented by manganese-bearing clays) 

 which in its original condition must have been of very similar 



