234 



BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



number of stages, yet, in the present state of knowledge it seems 

 that, in so far as the large carbonate veins are concerned, we must 

 divide these into two types — a class of ankerite (including ferriferous 

 dolomite) — chalcopyrite veins for which, taking a name from the 

 oldest and most important mine of the type, at Iron Mountain, 

 Mont., we may designate the Amador type, and a class of siderite 

 veins with tetrahedrite or galena, more closely allied to the valuable 

 lead-silver veins of the Coeur d'Alene district. Disregarding varia- 

 tions in size and in relative proportions between gangue and valuable 

 metallic minerals we may designate the latter the Yankee Boy type. 

 Both of these may graduate, by different paths, into the typical 

 Coeur d'Alene lead-silver deposit. 



The siderite is easily destroyed by oxidation, yielding gossans of 

 limonite more or less darkened by manganese oxide. 



The siderites and other carbonate minerals from this region are 

 being analyzed from time to time in the Museum laboratory, and such 

 analyses as have been completed to date are here stated. 



A specimen from the Castle Rock property, south of Wallace, col- 

 lected by E. L. Jones, jr., in 1912, consists of massive rather fine- 

 grained buff to bluish siderite cut by later seams of quartz and con- 

 taining thoroughly disseminated patches of chalcopyrite and tetra- 

 hedrite. The bluish color of a part of the carbonate may be due to 

 finely disseminated sulphides. The analysis gave the following com- 

 position, recalculated to 100 per cent after deducting a little gangue. 



Siderite, Castle Rock prospect 

 (Earl V. Shannon, analyst) 



This specimen is therefore predominantly iron carbonate with a 

 moderate amount of manganese and magnesium carbonates and very 

 little lime carbonate. 



The second specimen analyzed and found to be siderite is a speci- 

 men from the Hemlock dump collected by Mr. Calkins in 1912. 



This is a mass of moderately coarse granular buff siderite containing 

 some later galena and a little pyrite and quartz. The analysis gave 

 the following results. 



