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Character and Distribution of Nonclastic Minerals in the Searles Lake Evaporite Deposit California

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Character and Distribution of Nonclastic Minerals in the Searles Lake Evaporite Deposit California Character and Distribution of Nonclastic Minerals in the Searles Lake Evaporite Deposit California By GEORGE I. SMITH and DAVID V. HAINES I CONTRIBUTIONS TO GENERAL GEOLOGY GEOLOGICAL SURVEY BULLETIN 1181-P Prepared in cooperation with the State of California, Resources Agency, ' Department of Conservation, Division of Mines and Geology -A UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1964 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director The U.S. Geological Survey Library catalog card for this publication appears after page P58. For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 CONTENTS Page Abstract..---.---------------------------------------------------- PI Introduction-____________-___-___----_--_-______-____--_______-___ 3 Acknowledgments ____-_____---_-__--__--_----__-_______---____..__- 4 Mineralogy __________-_---_---------_-_--_----_-------_--__-_-____ 6 , Minerals associated with saline layers____________________________ 8 Aphthitalite.. __-____---_----_---_--___---_---__-_________ 8 Borax-----.--------------------------------------.------- 10 Burkeite__.______--____-_.._-___-._-__.____..._..______ 12 Halite ------------------------------------------------- 14 Hanksite.-_------------_-----_-------__----------_----__- 16 Nahcolite__-___-_---_-_______-___-___---_____-___-_-____ 18 ^ Sulfohalite-.--------------------------------------------- 19 Teepleite._-----------------_----_------_-------_---_-.-.- 20 ,- Thenardite...-----__-_----__-------__------__.---.--__--- 20 Tincalconite______________________________________________ 21 < Trona---_--------_---------------_-------------------_. 21 Minerals associated with mud layers ----------------------------- 24 Adularia. ________________________________________________ 24 Analcime._ _______________________________________________ 25 Aragonite__._.--___-._-___--_-.---___-__.______-_______- 25 '. Calcite.-------------------------------------------------- 25 Dolomite...----_-----.-__-_--------__-----_------.-_----- 26 * Galeite---.-----__----.__--_-------_------._-----.-------_ 27 Gaylussite.---___-___-____--_-_-______--___-_____-___--__- 27 Mirabilite.----------------_----.---._----_-.-----_------- 30 Northupite._..-__._._._._...__-__._.____...-____..__-.-._ 30 ' Phillipsite--------.---.-__---_--._.-.---.-.---.-.-.------- 31 Pirssonite __ _____________________________________________ 31 Schairerite..______________________________________________ 32 ., Searlesite.._______________________________________________ 33 Tychite._.--..---.-_-...-...-..-..-_..--._-..._..-..-.--_ 33 '> Summary of mineral occurrences. _______________________________ 33 Overburden Mud__---------------------------------------- 34 ^ Upper Salt ------------_-----_----..--.---------..------ 34 Parting Mud--..-----.-._.-.--..---.---.-----_----------- 34 Lower Salt__-___--__--____________________._______________ 55 ^ Bottom Mud.__________________________________________ 36 Mixed Layer......________________________________________ 37 ~/ Significance of variation in physical character of minerals.-.-------- 38 Differences in crystal sizes._________________________________ 38 ".J Differences in development and preservation of crystal faces.._- 40 Differences in crystal habit. ________________________________ 40 Halite.._.---....-_...._--.__.._...__---_---.---..-.-- 41 Borax_----________-___--___.____..__________._.______ 42 Trona _____________________________________________ 42 ,__ Hanksite.-_--_.-.--._-_________-_.___.__._-___.___--- 43 in IV CONTENTS Page Lake history indicated by character and distribution of minerals----.--.- P44 Minerals in the saline layers. _____:_____________________________ 46 Mixed Layer.----.---------------------------------------- 47 Saline layers in Lower Salt--_____--_--_-______-__.______-___ 47 Upper Salt________-----__--_-__----__-----__--____-____ 50 Minerals in the mud layers- --._----__.--_____----____-_______-_ 51 Mixed Layer____-_--__-_------_------------------_----_--- 53 Bottom Mud___--_.___.______-____---_--__-__--__---_.__ 53 Mud layers in Lower Salt.--.------....-._---_-____________- 54 Parting Mud________-_-----___________---_-_--__--_-__-_ 54 Overburden Mud._________________________________________ 55 References cited.._________________________________________________ 55 ILLUSTEATIONS Page FIGURE 1. Index map showing location of Searles Lake, Calif_________ P3 2. Subsurface stratigraphic units in the Searles Lake deposit- _ __ _ 5 3. Location of drill cores cited-_____________________________ 9 4-14. Photographs of: > 4. Borax crystals showing habits most commonly noted in Searles Lake__--_-____-___-___------_--_----_.-_ 10 5. Elongated borax crystals.__________________________ 11 6. Beds of trona separated by a lens of borax.___-__--_._ 12 7. Thin section across the bed of trona and borax shown in figure 6_--._---_----------------------------- 13 8. Large halite crystals in a vug___-________--____.__-_ 15 ^ 9. Hanksite crystals found in Searles Lake showing vari­ ation in habits-.-.--.----_______________________ 16 * 10. Hanksite and borax crystals._______________________ 17 \ 11. "Fishtail" twinned nahcolite crystals. _-___._._______ 19 12. Two forms of tincalconite. _________________________ 22 13. Trona blades penetrating borax.____________________ 24 14. Thin beds of aragonite in the Parting Mud.__________ 26 15. Sketches of relations between gaylussite and laminated muds. 29 f^ 16. Phase diagrams of the system NaHC03-Na2 C03-Na2SO4- NaCl-H2Oat 20° and 14° --._.....-..-...--..__-.-. 48 CONTRIBUTIONS TO GENERAL GEOLOGY CHARACTER AND DISTRIBUTION OF NONCLASTIC MIN­ ERALS IN THE SEARLES LAKE EVAPORITE DEPOSIT, CALIFORNIA By GEORGE I. SMITH and DAVID V. HAINES ABSTRACT The Searles Lake evaporite deposit, California, near the southwest corner of the Basin and Range province, was formed by a succession of late Quaternary lakes that filled the basin and then either shrank to form saline lakes or desic­ cated. The deposit crops out at the surface as a bed of nearly pure halite that covers an area of about 12 square miles; beneath the surface it consists of inter- bedded salines and muds that lie nearly flat and cover an area of about 40 square miles. This paper summarizes the areal and stratigraphic distribution of the nonclastic minerals in the deposit, correlates their characteristic forms with the stratigraphic units from which they came, and deduces the depositional history responsible for this distribution. A total of 25 nonclastic mineral species occur in Searles Lake; 10 of these species were first found in a natural state in this deposit. In terms of anions, 9 of the 25 minerals contain sulfate ; 8, carbonate or bicarbonate ; 7, chloride ; 4, bor- ate; 3, fluoride ; 3, aluminosilicate; and 1, borosilicate. In terms of cations, 20 of the 25 minerals contain sodium; 6, calcium ; 3, magnesium ; and 4, potassium. The minerals containing calcium and magnesium are chiefly carbonates ; the minerals bearing sodium and potassium may contain any of the listed anions. Ten of the 25 minerals contain water or hydroxyl ions. The distributions and characteristic forms of these minerals are different in each of the stratigraphic units. The Overburden Mud (late Recent) consists predominantly of interbedded dark-brown mud and cubo-octahedral or water- rounded halite. The Upper Salt (early Recent) consists chiefly of thick beds of cubo-octahedral crystals of halite, pyramidal crystals of hanksite, megascopic to microscopic crystals of acicular trona, and thin beds of borax. The Parting Mud (late Wisconsin) consists of mud containing subhedral to anhedral crys­ tals of gaylussite and pirssonite, with subhedral to massive borax at the top, and local concentrations of microscopic crystals of dolomite, aragonite, halite, gaylus­ site, and pirssonite. In the Lower Salt (middle Wisconsin) each of the seven saline units and six mud units has a distinct mineral character. In the upper two saline units, intermixed aggregates of fine-grained and coarse-grained acicur lar trona predominate, but cubo-octahedral halite is locally abundant; the two thin mud layers underlying these units contain subhedral to anhedral mega­ scopic gaylussite, a smaller percentage of euhedral pirssonite, and microscopic PI P2 CONTRIBUTIONS TO GENERAL GEOLOGY crystals of both. The underlying two saline units consist chiefly of fine-grained trona, cubo-octahedral halite, and finely crystalline burkeite; the mud layers below them contain megascopic and microscopic crystals of gaylussite and nor- thupite and prismatic crystals of borax. The lowest three saline units are com­ posed chiefly of intermixed aggregates of fine-grained acicular trona and coarse­ grained bladed trona ; the two mud layers that separate them contain fine-grained aragonite and northupite and megascopic gaylussite. The Bottom Mud (early Wisconsin), which is about 100 feet thick, is composed chiefly of mud containing subhedral to anhedral gaylussite, but also contains small quantities of halite, thenardite, nahcolite, dolomite, calcite, tychite, pirssonite, northupite, borax, trona, mirabilite, analcime, adularia, and searlesite. The Mixed Layer (Illi- noian? and Sangamon?) is a series of interbedded muds and salines that has not been well explored. The layer consists chiefly of cubic halite, acicular trona, and muds, which here, as well as throughout the rest of the deposit, are composed of microscopic crystals of evaporites,
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