2 PROCEEDINGS OF THE NATIONAL MUSEUM vol.74 



the surface and the surface ore was very rich, assaying 300 ounces of 

 silver and 3 ounces of gold to the ton. Adjacent to the veins the 

 schists are commonly rather highly altered and frequently silicified 

 and cut by veinlets of silica and pyrite. The walls of the veins are 

 more or less indefinite and gradational.'* 



ORES 



The richest specimens at hand consist of massive silver minerals, 

 somewhat fractured and traversed by thin fillings of quartz. These 

 contain a few cavities lined by crystals of miargyrite over which there 

 may or may not be a discontinuous coating of clayey substance. 

 The massive material consists principally of massive miargyrite. 

 Hulin writes that miargyrite is the most abundant and important 

 silver mineral of the region, but that stylotypite is only slightly less im- 

 portant. He says that the latter mineral is not apparent in the hand 

 specimens, since it ordinarily occurs in minute irregular or rounded 

 grains, commonly microscopic in size, which are usually entirely sur- 

 rounded by miargyrite. The stylotypite is further almost invariably 

 associated with chalcopyrite and occasionally with argentiferous born- 

 ite. Hulin defines stylotypite as a silver-bearing bournonite with the 

 formula 3(Cu2,Ag2,Fe)S.Sb2S3, which is the formula given for this 

 mineral by Dana. It was identified by him in polished surfaces 

 under reflected light and is described as brittle, metallic, dark gray 

 in color, and with a black streak. Microchemical and blowpipe tests 

 indicated the presence of silver, iron, antimony, and sulphur in the 

 Randsburg mineral. On polished sections it is faintly gray and 

 slightly lighter in color than the miargyrite. 



Wherry and Foshag ^ give as the formula for stylotypite simply 

 3Cu2S.Sb2S3. Since the composition of this mineral is so incom- 

 pletely known it was hoped that enough of the Randsburg material 

 could be obtained for analysis. The coarse-grained massive high- 

 grade ore was sawed and polished and etched on the polished surface 

 with nitric acid. It was foimd to consist almost entirely of miargyrite 

 which was unattacked by the nitric acid. There was present, how- 

 ever, a little interstitial material which etched bronzy and probably 

 is the mineral identified as stylotypite by Hulin, but it was in such 

 small amount and so intergrown with miargyrite as to render the 

 separation of a portion for analysis impracticable. 



The majority of the specimens of the lot consists of a breccia of 

 fragments of dark gray fine-grained siliceous material the open inter- 

 stices of which are lined with a layer of white quartz covered with a 

 druse of minute transparent quartz crystals. It is resting upon the 



* Uulin. Geology and Ore Deposits of the Randsburg Quadrangle of California, p. 112. 

 » Edgar T. Wherry and W. F. Foshag. A New Classification of the Sulphosalt Minerals. Journ. 

 Wash. Acad. Sci., vol. 11, No. 1, pp. 1-8, January, 1921. 



