480 Brannt r — Minerals Associated with Diamonds and 



Art. XXXIX. — The Minerals Associated zoith Diamonds 

 and Carbonados in the State of Bahia, Brazil ; by J. C. 

 Branner. 



Several persons have already studied and written upon the 

 minerals associated with diamonds in Brazil.* Most of the 

 papers, however, have been based upon the concentrates found 

 in washing for diamonds in the Diamantina district in the 

 state of Minas Geraes. Comparatively little has been said of 

 the general geology of the Brazilian diamond region, and that 

 little has not always helped to clear np the questions that arise 

 in connection with the origin of the diamonds. Indeed the 

 geology of the diamond district of Minas Geraes is far from 

 being simple, and no reconnaissance has yet been made that 

 shows the general structure and relations of the rocks and 

 minerals. The diamond district of Bahia is north and a little 

 east of Diamantina and about 650 kilometers distant on an air 

 line. 



The paper published by Damour in 1853, two by Gorceix 

 published in 1884, and one by Uussak published in 1899, deal 

 with the minerals found with the diamonds in Bahia, but none 

 of these papers contains anything on the stratigraphy of that 

 district. Indeed, up to the year 1905 practically nothing was 

 known in regard to the general geology of the Bahia diamond 

 region. In that year Professor Derby made a trip into the 

 region for the state of Bahia, and prepared a short report to 

 the government on its geology. That paper was published in 

 Portuguese at Bahia, and, on account of its importance, it was 

 translated into English and republished in Economic Geology 

 (vol. I, pp. 134-142, Dec, 1905), and again in the Smithson- 

 ian Eeport for 1906 (pp. 215 to 221). 



The paper by Derby represents our knowledge of the 

 geology and mineralogy of the diamond regions of Bahia 

 up to i90T, when I visited and traveled through that region for 

 some months. 



General geology of the diamond regions of Bahia. — I have 

 already published brief sketches of the geology of the Cha- 

 pada Diamantina of Bahia, f and only enough will be repeated 

 in this place to give an idea of its broad features. 



* Boue\ Bovet, Brongniart, Damour, Derby, Dufrenoy, Eschwege, Gorceix, 

 Hussak, Moissan, and others. 



f The economic geology of the diamond-bearing highlands of the interior 

 of the state of Bahia, Brazil. Engineering and Mining Journal, lxxxvii, 

 981, 1031. May, 1909. 



Outline of the geology of the black diamond region of Bahia, Brazil. 

 Australasian Assoc, for Adv. Sci. 1908, 324-328. Brisbane, 1909. 



