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,aheolite ng o- ity 2.., Cis pres- the eav- in pro- ercfore. hcrelo- -motion dvanta• :II 22 is ito the 3 is ce- d adja- lhe in- forma- is pro- m the refera- oC the :as the ~ point ing 26 ie cas- mcans nds of rfora- 1 wrlF :o Q. as lift :coon com- near ofin- :sircd alum 0°F is then ns 25 from filled 'e 32. pro- ~tion ying i the pro- ~ugh tom 27. ad- at a ere 26 re- thc ah- ~ Ier Or n- tc ~r r 5 31 or other permeabilized zone. In such a cox, aque- ous Iluid may be injected into the formation 10 through one well and produced from [he formation through a separate well. Both FIGS. 3 and d illustrate the process after a cav- ity 21 or 31 has been formed. It should be understood that in many cases, initial treatment will be confined to a substantially cylindrical wellbore and that the cavern is formed only after a period of leaching has expanded the wellbore radically. We claim as our invcntiom 1. In a method for solution-mining heat sensitive water-soluble sodium bicarbonate minerals from a sub- surface bicarbonate mineral containing oil•shale for- ma[ion of the type wherein a hot aqueous fluid is in- jcc[ed in[o [he formation to leach bicarbonate mineral therefrom, the improvement comprising: injec[ing steam in[o the formation at a temperature greater than 250°F to leach water-soluble mineral from the formation and thereby create a leached zone; maintaining the temperature of fluid in the leached zone at a temperature greater than 250°F; and adjusting pressure in [he leached zone to an optimum pressure at which the sodium mineral carrying ca- pacity of water at the selected temperature is a maximum. 2. The method of claim 1 further comprising produc- ing liquid containing dissolved sodium bicarbonate from a liquid layer adjacent the bottom of the leached zone through a production tubing string using artificial lift means to lift the liquid to the surface. 3. The method oC claim 2 further Comprising with- drawing gas containing COr from a gas layer adjacent the top of the leached zone. 4. A method for solution•mining nahcolite from a subsurface oil-shale formation comprising the steps o(: 3,779,602 6 traversing a nahcolite-containing zone of the oil- shalc formation x~ith a well; estc nding a production string of tubing into the well to a point adjacent the bottom of the nahcolite- 5 containing zone; cxlending an injection tubing string info the well to a point adjacent the top of the nahcolite-containing zone; injecting steam into contact with the nahcolite con• 10 raining zone through the injection tubing at a tem- perature such that upon contacting the formation at least some of the steam condenses to liquid which liquid (lows to the bottom of the nahcolite zone leaching nahcolite therefrom; IS producing nahcolite containing aqueous liquid from the nahcolite zone through the production tubing; controlling the rate and temperature of steam injec- tion to maintain a selected temperature of aqueous liquid adjacent the bottom of the nahcolite zone; 20 adjusting the pressure in [he aqueous liquid adjacent the bottom of [he nahcolite zone to an operating pressure substantially equal to that pressure at which the amount of sodium mineral the aqueous .,5 liquid can carry at the elected temperature is a maximum; and maintaining the pressure in the aqueous liquid adja- cent the bottom of the nahcolite zone substantially constant at the operating pressure. 70 5. The method of claim 4 wherein the operating pres- sure is a pressure less than that required to hydrauli- cally fracture the formation. 6. The method o(claim 5 wherein the operating pres- sure is greater than the pressure at which the rate of 35 nahcolite decomposition is a maximum at the selected temperature. 40 45 50 55 60 63