36 BULLETIN 61, U. S. DEPARTMENT OF AGEICULTUEE. 



rich in potash, and those in which solutions rich in sulphates and coming from deep- 

 seated sources rose through fissures and deposited their mineral content where tem- 

 perature and pressure conditions favored deposition. In the first type the alunite 

 has been deposited more or less in situ. In the second, the alunite originated at 

 depth and was deposited close to the surface. Deposits of the first class are dissemi- 

 nated, while in the case of the second type the deposits are concentrated. To the 

 first tjTpe belong the Goldfield, Camp Alunite, Rabbit Hole Spring, Cactus Range, 

 and Cuprite occurrences. To the second belong the Marysvale occurrences. Alunite 

 is a possible source of potash.^ Of the known occurrences of this mineral in the 

 basin region, the Marysvale deposit is the only one which shows possibilities of com- 

 mercial exploitation. The results of work upon this deposit will be looked forward 

 to with interest. In view of the widespread solfataric action, in past as well as present 

 geologic periods, it is not improbable that other deposits of alunite will be discovered 

 in this region. 



ALKALI CRUSTS AND EFFLORESCENCES. 



It is diflficult to draw a sharp line between deposits of this type, playa deposits, 

 and deposits resulting from the desiccation of lakes. I have included under this 

 head, however, all surface deposits which have originated during present times and 

 which are of inconsequential thickness. These deposits have their origin in the 

 evaporation of shallow bodies of rain water, or in the action of seepage waters in bring- 

 ing dissolved salts to the surface, either by springs or capillarity. Hot springs are 

 also responsible for crusts in their immediate vicinity. 



These occurrences are usually characteristic of the playas or sinks. In Table 

 XVIII (Appendix) are presented analyses of crusts taken from a niunber of locali- 

 ties. The average of these analyses shows the ions in the following order: Na, 30.23; 

 Ca, 2.29; K, 1.68; Mg, 1.38; and the acid radicals SO4, 30.39; CI, 21.64; HCO3, 6.22; 

 CO3, 6.13. The average analysis shows the predominance of sodium. The ratio of 

 Bodiiun to potassium is 19.1 to 1. The sulphate radical is in excess of the chlorine. 

 Carbonates and bicarbonates are usually present and in a few cases are in large excess 

 of chlorides and sulphates. Sodium chloride and sulphate are the two compounds 

 most abimdant. Potassium is usually small in amount, although in a few of the 

 Utah crusts this element. is present in percentages ranging from 3 to 6. 



In Table XIX (Appendix) are given a number of analyses of salt crusts and waters 

 from Railroad Valley, Nev. The sam.ples were taken by E. E. Free and J. Hance. 

 They were analyzed by A. R. Merz for the percentages of soluble salts and the potash 

 content of the soluble salts. The sam.ples represent a general sm-vey of this area. 

 They show, on the whole, a high content of potash. Six crusts and one brine were 

 analyzed by J. A. CuUen, and his results are given in Table XX (Appendix). They 

 show that sodium chloride is the compound most abundant, with potassium chloride 

 usually next, followed in order of abundance by sodium sulphate, sodimn bicarbonate, 

 sodium carbonate. The average ratio of sodium to potassium is 5.7 to 1. The presence 

 of potassiimi compounds in these crusts first attracted attention to this area and led 

 to the exploratory work done by the Railroad Valley Saline Co. 



The origin of salines of this nature is simple. They may be said to be derived from 

 the weathering of rocks and the liberation of contained salines in the drainage area 

 of the tributary basin. Through the agency of surface and underground waters they 

 are collected in low places. 



Such deposits, excepting the borates, which have been discussed previously, have 

 no commercial value. The complex mixture of salts and the superficial nature of 

 the deposits are the reasons for nonexploitation. In a few local cases salt has been 

 gathered from crusts of this nature and marketed . No serious proposal has been made, 

 ae far as I am aware, for the exploitation of alkaline crusts rich in potash, although 

 the aggregate amount of potash in an area like that of Railroad Valley must be very 

 large. The chief interest in these deposits lies in the insight which they give into 

 the chemical nature of the salines at present accumulating in the arid basins of the 

 Great Basin. 



PLAYA DEPOSITS. 



Perhaps one of the most common topographical features is the desert basin. The 

 basin may be circular, elliptical, or gi-eatly elongated on one axis, forming a long, 

 narrow valley. Such basins usually have in their lowest part a level area devoid of 

 vegetation, sometimes covered with saline crusts, but more often simply consisting 

 of a rain-puddled sheet of clay. To this central portion the term "sink" or "playa" 



» For the conditions under which potash is made available in alunite see Cir. No. 70, Alunite as a source 

 of Potash, Bureau of Soils, U. S. Dept. of Agr. For use of alunite as a fertilizer see Cir. No. 70, Alunite and 

 Kelp as Potash Fertilizers, Bureau of Soils, U. S. Dept. of Agr. 



