REPORT OF THE DIRECTOR I9II I79 



preference, it forms in the new aggregates of sericite, carbonates and 

 chlorite so common in altered rocks; but it also occurs in the fresh 

 original minerals of the rocks, as in quartz, feldspar, horneblende and 

 pyroxene. It is common to find small, sharp crystals embedded, for 

 instance, in perfectly clear quartz grains, which show no break in 

 their optical orientation around the secondary crystal, proving that 

 the genesis is by purely metasomatic processes, and not, as may be 

 advocated in the case of crystallization in soft aggregates, by the 

 mechanical pressure of the growing crystal" (page 615). "The 

 pyrite crystals are often bordered by a small rim of calcite or quartz ; 

 and little bunches of sericitic fibers may adhere to them, when form- 

 ing in quartz" (page 616). Of chlorite he says, ''This mineral, 

 replacing amphibole, pyroxene and biotite, is commonly found in 

 altered vein-rocks, but ordinarily is only a transition form, often 

 abnormally rich in iron, which these minerals assume under the 

 influence of waters slightly charged with carbon dioxid before their 

 final conversion into sericite and carbonates. The chloritic altera- 

 tion is most important in the group of the propylitic veins. Under 

 the influence of strong alkaline carbonates and carbon dioxid, 

 chlorite can probably not exist " (page 610) . Later he. quotes 

 Rosenbusch on the development of the propylitic facies involving 

 **' a considerable development of sulfids," and says, '' The waters 

 principally active during the formation of the propylitic veins prob- 

 ably contained only a small amount of carbon dioxid and very little 

 lime, but may have been rich in sulfuretted hydrogen " (page 645), 

 Finally, in summarizing he says, '' I believe that the majority of 

 fissure veins are genetically connected with bodies of intrusive rocks, 

 even when the actual deposits are contained in overlying surface 

 lavas " (page 691). 



The descriptive portions of these passages might be applied with 

 little change to the pyrite, chlorite and sericite of the deposits under 

 consideration, and although propylitic alteration is a feature of 

 surface flows, it seems to shed light upon the deeper seated operation 

 here dealt with. In both cases waters heavily charged with H.S 

 are the active agent, and pyrite is an important product. The 

 accompanying chlorite is considered by Lindgren to be unstable in 

 the presence of much carbon dioxid, altering to sericite and car- 

 bonates. In the present case, deficiency of carbon dioxid doubtless 

 accounts for the relative stability of the chlorite, although at one 

 point, the Hendricks mine, the process has gone to completion, with 

 the formation of sericite, calcite and quartz. Thus in the pyrite 



