abstracts: geology 637 



GEOLOGY. — A reconnaissance of the Pine Creek District, Idaho. Ed- 

 ward L. Jones, Jr. U. S. Geol. Survey, Bull. 710-A. Pp. 36, 

 pi. I. 1919. 



The Pine Creek district, Idaho, lies immediately west and south of 

 the Wardner district of the Coeur d'Alene region. The Pine Creek 

 drainage basin is underlain chiefly by sedimentary rocks of Algonkian 

 age, termed the Belt series. These rocks are intruded by small black 

 dikes, mainly along fault's. Deposits of well-rounded gravel of Tertiary 

 age cap many of the low hills adjacent to Coeur d'Alene River. Ex- 

 tensive faulting has occurred in the Pine Creek district; all these faults 

 are of the normal type. 



The ore deposits of the Pine Creek district are metasomatic fissure 

 veins and fissure fillings, with gradations between the two types. The 

 veins that show metasomatic replacement are best developed in shear 

 zones along major faults; the fissure fillings are best developed along 

 minor faults or in zones of moderate shearing. The veins are chiefly 

 valuable for their zinc, lead, silver, and antimony content, though some 

 contain also gold and copper. These veins are probably best classified 

 on the basis of their dominant metal or mineral content, into zinc-lead, 

 antimony, and siderite veins. 



The best examples of the metasomatic fissure veins are those of the 

 zinc -lead type. The most valuable ore is a fine-grained aggregate of 

 sphalerite and galena in which there are commonly fragments of un- 

 replaced wall rocks. Pyrrhotite accompanies the ore and in places is 

 the chief mineral. Chalcopyrite is usually present in small amounts. 



The antimony veins differ markedly from the other veins of the dis- 

 trict in mineral composition. The principal metallic sulphide is stib- 

 nite. Pyrite is a common constituent of these veins, and here and 

 there they contain sphalerite. 



Manganiferous siderite veins occur in the southern part of the Pine 

 Creek basin. These veins are simple fissure fillings. No important 

 ore bodies have yet been developed in any of them. 



The primary sulphide minerals of the Pine Creek district are galena, 

 sphalerite, pyrite, pyrrhotite, chalcopyrite, tetrahedrite, stibnite, and 

 arsenopyrite. The minerals that resulted from the oxidation of the 

 sulphides are cerusite, malachite, massicot, pyromorphite, and chal- 

 cocite. 



Mines and prospects are described. R. W. Stone. 



