l'.ui 0, A. Derby — Gold-bearing Lod\ of Passagem. 



that the sulphide invasion took place before the complete 

 cessation of the formation of tourmaline. 



A partial analysis of one of the sericitic masses, made with 

 the view of determining the constituents that cannot he 

 referred to the original feldspar crystal, gave 4'14$ of com- 

 bined water, 4'1$ of carbonic acid (combined with lime as 

 calcite) and distinct traces of fluorine, and it is thus evident 

 that these elements played a part in the tourmalinization of 

 the original pegmatitic vein and in the alteration of its felds- 

 pathic contents. 



The Passagem lode thus presents evidence of three distinct 

 processes of filling, and the succession of events in its forma- 

 tion may be summarized as follows: 



First — An extensive fissure opened by stress along (above, 

 below and across) a bed of brittle rock (quartzite) enclosed' 

 between more tenacious schists, was closed by an invasion of 

 pegmatite running off into clear quartz. At this stage the 

 lode contained only the minerals characteristic of a granite 

 magma such as is represented in the neighborhood by a boss 

 of granite ; or, possibly, some others that may have been 

 formed near the contact through reactions with the country 

 rock. 



Second — A subsequent stress, acting in substantially the 

 same place and manner as the first, fractured this pegmatitic 

 quartz, rendering it accessible to a pneumatolitic action charac- 

 terized by silica, boron, water vapor, carbonic acid and fluorine 

 ("after effect" of the granitic eruption?), which filled its As- 

 sures with tourmaline, sericiticized the feldspar of the pegma- 

 tite wherever fissures, often quite minute, permitted access to 

 it, and probably produced the characteristic contact phenom- 

 ena noted by Hussak. 



Third — A third stress, coming near the end of the second 

 phase of the lode, fractured the tourmaline filling and gave 

 access to a pneumatolitic action characterized by sulphur, 

 arsenic, metallic oxides and metals (gold and silver), which 

 filled the fissures of the lode, invading to some extent its pre- 

 existing portions, and probably also some of tli3 adjacent and 

 enclosed country rock. 



Servigo Geologico e Mineralogico do Brasil, 

 Rio de Janeiro. May 8, 1911. 



