Koenig — Mohatvkite, Stibio-domeykite, Domeykite, etc. 439 



Akt. XLII. — On Moha/wkite, Stibio-domeykite, Domeykite, 

 A Igodonite and some artificicd copper-arsenides ; by George 

 A. Koenig. 



The knowledge of the existence of copper arsenides in the 

 Keweenaw copper formation is nearly as old as the mining 

 operations in this region themselves. In the matter of occur- 

 rence there are two points to be noted : (1) The arsenides are 

 not found in the bedded deposits of native copper, but always 

 in fissures, intersecting the beds. (2) These veins have thus 

 far only been observed in the lower beds, near the foot of the 

 formation to the southeast. Arsenic, however, is found in the 

 smelted and refined copper of all the mines. ■ This element is a 

 minimal amount in the copper from the Great Conglomerate 

 of the Calumet and Hecla mine and becomes a maximum in 

 the copper from the amygdaloid beds of the lower measures, 

 on which the Mohawk, Wolverine, Arcadian, Sheldon-Columbia, 

 Isle-Royale, Atlantic, Baltic, Champion, etc., are located. The 

 Sheldon-Columbia location near the shore of Portage Lake in 

 the village of Houghton was the first mine which furnished 

 copper arsenides, notably domeykite. The larger part of the 

 specimens in collections come probably from this mine. Whit- 

 neyite was found in a quartz vein in dark melaphyr, not far 

 from the present Mohawk, but the existence of any copper rock 

 was not suspected at that time at that point. Several masses 

 of domeykite have been found in the drift on the Hancock 

 shore of Portage Lake, very much decomposed, cuprite and 

 arsenates being the chief products. In the spring of 1898 the 

 opening of a new street in East Houghton on the old Sheldon- 

 Columbia location, disclosed a quartz vein containing some foli- 

 ated domeykite. Many good specimens were gathered and 

 have come into collections. A similar vein has been known 

 for years on the old Huron location, now the southern end of 

 the Isle-Royale property. Algodonite was found in the 

 Pewabic mine, located on the Quincy amygdaloid bed and 

 which lies about 5000 feet higher than the Isle-Royale amygda- 

 loid. In developing the Mohawk property a cross vein at 

 right angles to the copper-bearing amygdaloid was met in 

 December, 1899. This cross vein was from 12 to 15 inches 

 wide when struck, but has since shown very varying dimen- 

 sions. In a gangue of quartz and calcite the copper arsenides 

 have been found in this vein more abundantly than in any of 

 the locations mentioned above. Early in January Mr. Fred. 

 Smith, Superintendent of the Mohawk mine, sent me a solid 

 piece weighing from 4 to 5 pounds, with the request to make 



Am. Jour. Sci. — Fourth Series, Vol. X, No. 60. — December, 1900. 

 29 



