738 ABSTRACTS OF PAPERS 



GEOLOGY OF THE CHIBOUGAMAU REGION, QUEBEC, CANADA 

 BY ALFRED ERNEST BARLOW 



{Abstract) 



The region described is underlain by rocks of Arclisean or pre-Cambrian 

 age. These are included in the Keewatin, Laurentian, and Huronian forma- 

 tions. In addition, an intrusive rocli which seems peculiar to this area has 

 been referred to the gabbro-anorthosite, because although it is of gabbroic 

 type, there is in general a marked absence or paucity of the ferromagnesian 

 minerals usually so abundant in gabbros. In this respect, it resembles the 

 anorthosite formerly classified as upper Laurentian, but is more acidic. The 

 geological relations of these formations will be discussed, as also the origin 

 and mode of occurrence of gold-bearing quartz veins, asbestos-bearing serpen- 

 tines and certain deposits of chalcopyrite, pyrrhotite, and magnetite. 



OCCURRENCE OF SILVER, COPPER, AND LEAD ORES AT THE VETA RICA 

 MINE, SIERRA MO J ADA, COAHUILA, MEXICO 



BY FRANK R. VAN HORN 



{Abstract) 



These ores occur on the contact or a short distance below the contact of an 

 acid breccia with an underlying limestone of Cretaceous age. There are some 

 indications of a fault plane between the two rocks, such as clay selvages and 

 slickensides. There are two types of ore, a silver-lead and a silver-copper 

 series. In the former group, the minerals are all oxidized and consist chiefly 

 of argentiferous cerussite along with native sulphur and some gypsum. The 

 bulk of the ores from this mine, however, seems to belong to the silver-copper 

 group and contains sulphides as well as oxidized minerals. Minerals noticed 

 here were chalcopyrite, chalcocite, covellite, along with native copper, mala- 

 chite, azurite, cuprite, and gypsum. Another zone consisted of a siliceous 

 limestone containing up to 10 per cent of barite which was impregnated with 

 cerargyrite and native silver. Here the copper content was smaller and rarely 

 exceeded 2 per cent. Some three yars ago, a fault was discovered in the 

 northern part of this "silver-lime" ore body. Along this fault plane silver 

 and copper minerals of great richness were found mixed with more or less 

 barite. Some of the minerals noticed M^ere native silver, argentite, proustite, 

 and pearceite which has been found in but two or three localities in the world. 

 At this point a mixture of erythrite and barite was also noticed, which seems 

 to be the first observation of cobalt minerals in the district. 



