538 GEORGE DAVIS LOUDERBACK 



few other places. These deposits are described with some detail in the 

 text of the Port Orford folio. In general, they may be characterized 

 as quartz veins — more rarely calcite-bearing — carrying some gold, 

 and frequently stained by iron oxides or iron and manganese oxides. 

 The less oxidized portions carry pyrites — in some cases a little galena 

 and arsenopyrite. They occur chiefly in the granular intrusives, 

 but are sometimes found in the sedimentary rocks — slates and sand- 

 stones. Occasionally they are associated with serpentine or dacite. 



Economically more important have been the placer mines of this 

 region, which have been worked since the early fifties. The chief 

 areas on the Port Orford quadrangle are along Sixes River and 

 the creeks above mentioned, corresponding closely to the distribution 

 of the best-developed veins in the Dillard and the associated intrusives. 

 It seems quite reasonable, therefore, to consider the gold as derived 

 from these formations. 



Effects 0} structure. — The minor economic importance of the aurif- 

 erous veins associated with the Dillard and its related intrusives, is 

 in large measure dependent on the character of the earth movements 

 to which these rock masses have been subjected. While the changes 

 they have undergone have been considerable, they have not been of 

 such a character as to favor the production of great lodes. Instead 

 of great fissures, there are innumerable fractures and faults of minute,, 

 small, and medium proportions, very local crushing, schistification, 

 or slate production. Minute veinlets and small veins are therefore 

 common. Rarely, however, does a vein maintain a uniform trend 

 or even its existence for any great distance, and the various irregular 

 small veins and " stringers" cannot be grouped into systems with 

 regular attitudes. The mapping shows that intrusive dikes and 

 masses exhibit the same characteristics. The only regularity to be 

 observed in the mapping seems to have been brought about by the 

 post-Cretaceous foldings which affected all the formations together. 



If the quartz-diorites shall later be shown to be older than the 

 Dillard, it may follow that some of the above deposits are pre- 

 Dillard. 



Copper. — Copper prospects have been found along the ridge near 

 Dodson Mountain southeast of Roseburg. The metal occurs in 

 chalcopyrite and malachite, in disseminated grains or bunches in. 



