LINDOHEN.] GOLD DEPOSITS OF WILLOW AND. ROCK CREEKS. 713 



the decomposed surface material does not always allow satisfactory 

 conclusions as to the character of a deposit. A large number of loca- 

 tions have been made in both districts, which, in fact, contain a very 

 great number of veins. The ordinary type of the "Willow Creek 

 deposits consists of one or more fault fissures, on both sides of which 

 there is a zone a few feet wide in which the country rock has been 

 thoroughly altered (see Chapter II) and impregnated with pyrite. 

 Along the main fissure, or, if there are two or more, chiefly along the 

 foot wall, there are narrow seams filled with sulphides (pyrite, zinc- 

 blende, arsenopyrite, and galena), which constitute the ore. The 

 altered country rock, though often studded with pyrite crystals, usu- 

 ally contains only $1 or $2 in gold, while the value of the solid sul- 

 phides in the seams may reach $100 per ton or more. The deposit 

 may thus be characterized as narrow veins of high-grade sulphide, 

 ore. There is usually but little gangue along these seams ; calcite 

 and quartz both occur. In other deposits the zone of altered diorite 

 or granite is traversed irregularly by numerous small seams carrying 

 arsenopyrite, blende, and galena, and in this manner the wider depos- 

 its of medium-grade ore are formed. The veins of Rock Creek are 

 generally wider than those of Willow Creek. 



The surface decomposition attains 50 to 100 feet in depth. In this 

 zone the vein matter forms a brown ferruginous mass, which contains 

 free gold and partly decomposed sulphides, often also lead carbonate. 

 In many cases the fresh sulphide ore is found less than 50 feet from 

 the surface. The fresh ore contains a very small percentage of free 

 gold, and sometimes, in rich ore, not even a color is obtained by the 

 pan. It follows from this that the amalgamation process, is, as a 

 rule, applicable only to the surface ores, though some veins will be 

 found to contain more free gold than others. At present the rich 

 ore all above $30 is sacked and shipped to smelters. 



The minerals consist of the following combination, so common in 

 the Boise Ridge: pyrite, arsenopyrite, zinc blende, and galena; chal- 

 copyrite is rare. The first two often occur as crystals. The zinc 

 blende is black, brown, or greenish-yellow, usually not crystallized. 

 The galena is less common than the others, and is considered an indi- 

 cation of rich ore. Ruby silver is reported as a rarity from the 

 Shamrock and the Lincoln. 



Shipping ore often contains 5 ounces of gold and 5 ounces of silver 

 to the ton. A sample of pyrite, arsenopyrite, and galena from one 

 of the best mines gave 0.85 ounce of gold and 28.35 ounces of silver 

 per ton, a total of $37.42. Some galena carries 60 to 70 ounces of sil- 

 ver, and generally also much gold. Much of the arsenopyrite and 

 zincblende is poor. The principal value appears to be in the pyrite 

 and galena. Of the extent and direction of the ore shoots but little 

 is known at present, but it is clear that the high-grade shoots are not 

 of great lateral extent and that they are rather irregular. 



