GEOLOGY ANÎ) ORE DEPOSITS OF StJ-AN 19 



regularly impregnated witli ilvaite, bornite, and clialcopyrite mingl- 

 ed with some iron-pyrite. In rare cases, some galena and magnetite 

 may also be associated. In no case has gold been detected by 

 the naked eye ^\ while the noble metal seems to be closely associat- 

 ed with copper-^ sidpyhides in a microscopic state, or in chemical 

 combination, but that portion impregnated with the ilvaite is poor 

 in gold content. Nowhere have these metallic sulphides been 

 observed to form any continuous bands or concentrated bodies. As 

 far as is known, they always occur irregularly dispersed in a 

 sporadic manner in the contact-metamorphosed limestones. 



In the western ore-body, especially in its southern and 

 w^estern portions, the limestone is highly metamorphosed into the 

 diopside-rock, colored a deep red, yellow, or even in some few 

 cases black, most of the coloring matter being undoubtedly ilvaite 

 and iron-oxide with which the hornfels appears to have been 

 transfused. Where the limestone and hornfels bear no ores, it 

 remains unaltered and unstained, and such barren portions, being 

 mixed up without any regularity with the decomposed workable 

 part, often remain protruding from the surface of open works. 



On the western margin of the western ore-body, not only 



1) Lately Mr. J. E. Poque described large cubes (2 inches) of pyrite from the Snettisham 

 District, Southeast Alaska. The crystals of gold, galena and chalcopyrite are set in the 

 superficial part of tlie remarkably large cubes of the pyrite which is striated on the surfac 

 with minute steps due to oscillatory combination of (210) and (100). The gold has crystal- 

 lized out in octahedron, cube and octahedron, dodecahedron and octahedron, and trapezo- 

 liedron and octahedron. These gold crystals lie half imbedded in the pyrite. The most 

 probable paragenetic relation is regarded as this: "The pyrite, when its present size was 

 nearly attained, sustained a deposition of crystallized gold upon its surface followed by the 

 precipitation of a small amount of chalcopyrite which, in turn, was succeeded by the formation 

 of galena. A further slight accretion of pyrite completes the development of the specimen ". 

 " On a Remarkable Cube of Pyrite carrying Crystallized Gold and Galena of Unusual 

 Habit". Smithsonian Mimcellaneom Collecliotis, vol. 52, Part 4 (Xo. 1882), 1909. 



From the above, we see that a part of gold at least is in native state in sulphide ore-^. 



2) The sulphide ores associated with the sulphide of copper are generally said to be 

 poor in the gold content. 



