ransome: wurtzite at goldfield 483 



is to be expected where ore containing zinc sulphide has been 

 deposited by acid solution at temperatures below 300°C. The 

 Goldfield ores, containing alunite and marcasite, two minerals 

 formed in an acid environment, are believed to have been de- 

 posited comparatively near the surface by the mingling of de- 

 scending waters containing sulphuric acid with ascending ther- 

 mal waters containing hydrogen sulphide and probably alkali 

 sulphides. Under such conditions, at least a part of the zinc 

 sulphide present, as was orally suggested to me by my colleague 

 Dr. J. B. Umpleby, might crystallize as wurtzite. 



To test this suggestion some of the material collected in 1908 

 from the workings of the Mushett lease on the Miss Jessie claim, 

 one of the few places in the district where zinc sulphide had been 

 found at that time, was reexamined. This ore was originally 

 described as follows: 



The ore of the Mushett lease on the Miss Jessie claim northeast of 

 the Red Top mine is structurally and mineralogically one of the most 

 interesting in the district. The proportion of sulphides to gangue is 

 greater than in most of the mines. The metallic minerals noted are 

 pyrite, famatinite, bismuthinite, sphalerite, and a dark-gray mineral 

 identical in appearance with that analyzed and described on page 116, 

 and probably like it the new species goldfieldite. This material is 

 rich in gold, specimens which to the naked eye show not a particle of 

 the native metal yielding over $8000 a ton on assay. The crustifica- 

 tion in the Mushett ore is not very regular, but the minerals have formed 

 in the following general succession: (1) pyrite; (2) famatinite, bismuthi- 

 nite, goldfieldite; (3) sphalerite; and (4) pyrite. The sphalerite in 

 some places forms botryoidal crusts over the prisms of bismuthinite, 

 which attain a larger size in this ore body than in other known occur- 

 rences in the district. 



The material forming the extreme outer crust of the nodular ores 

 of Goldfield or filling interstices between the altered and incrusted rock 

 fragments is in most places a soft mixture of alunite and pyrite.* 



The so-called sphalerite is dark reddish brown, forms crusts 

 rarely over half an inch thick and in places it shows a rather 

 indistinct radial fibrous structure. Reexamination shows that 

 a little marcasite is present as minute botryoidal aggregates on 

 some of the pyrite but is less abundant than in certain other 

 rich Goldfield ores. 



* Ransome, F. L., Op. cit., p. 165. 



