132 PROCEEDINGS OF THE ALBANY MEETING 



BARITE DEPOSITS OF MISSOURI 

 BY W. A. TAKR^ 



(Ahsti^act) 



The most important barite deposits of Missouri are tliose in Wasliington 

 County, in the soutlieastern part of the State ; but other important deposits 

 occur in the central part of the State. The barite which is mined in Washing- 

 ton County occurs as nodules and fragments, scattered through a deep, red, 

 residual clay. Associated with the barite are considerable chert and drusy 

 quartz and occasionally galena. The barite in the residual clay was derived 

 from veins in the Potosi and Proctor dolomites of Upper Cambrian age. The 

 barite is found only in association with these two formations. The barite is 

 believed to have been deposited by rising hot solutions. 



Presented in abstract extemporaneously. 



THE MAGMATIG SULFIDS^ 

 BY C. F. TOLMAN, JR., AN]) A. F. ROGERS 



(Ahstract) 



Our study of the magmatic ores has included a review of the field data 

 regarding these deposits and a study by all available microscopic methods of 

 numerous suites of specimens from Sudbury and Alexo. Canada ; Engels Mine, 

 Plumas County, and Friday Mine, San Diego County, California ; deposits at 

 Litchfield, Connecticut: the Golden Curry Mine, in Montana: certain of the 

 deposits in Norway, Saxony, and Bohemia, and the Ookiep mines, in South 

 Africa. 



As a result of these studies, we have concluded that the magnetic sulfid and 

 oxid ore minerals are formed after the original silicates of the rock, and at 

 their expense by replacement. Moreover, both euhedral and anhedral masses 

 of magnetite are later than the silicates. The formation of the ores, however, 

 was not accompanied by destructive pneumntolytic or hydrothermnl action, 

 for the solutions or miner alizers which brought in the ores were sufficiently 

 "in equilibrium" with the silicates so that replacement took place without the 

 development of secondary silicates by destructive action. 



It is shown definitely that extensive hornblendization of the pyroxenes pre- 

 cedes the formation of the ores, and that chlorite, tremolite, anthophyllite, 

 sericite, and serpentine are distinctly later than the magmatic ores. 



We attribute hornblendization and the formation of the ore minerals to a 

 late magmatic stage, and the alteration products mentioned above to a hydro- 



1 Introduced by E. B. Branson. 



2 A complete statement of the results of this investigation is in press: A study of the 

 magmatic sulfid ores, Leland Stanford .lunior University publications, University series 

 (1916). A short summary dealing with the Sudbury ores will appear in the Engineer- 

 ing and Mining .Tournal, Febrnaiy ,S, 1917, under the title : The origin of the Sudbury 

 ores. 



