The hydrogeochemistry of strontium in the Ranegras Plain groundwater basin
Item Type Thesis-Reproduction (electronic); text
Authors Dolegowski, John Richard,1951-
Publisher The University of Arizona.
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Link to Item http://hdl.handle.net/10150/191992 THE HYDROGEOCHEMISTRY OF STRONTIUM IN THE
RANEGRAS PLAIN GROUNDWATER BASIN
by
John Richard Dolegowski
A Thesis Submitted to the Faculty of the
DEPARTMENT OF HYDROLOGY AND WATER RESOURCES
In Partial Fulfillment of the Requirements For the Degree of
MASTER OF SCIENCE WITH A MAJOR IN HYDROLOGY
In the Graduate College
THE UNIVERSITY OF ARIZONA
1988 STATEMENT BY AUTHOR
This thesis has been submitted in partial fulfillment of requirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the library.
Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his or her judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author.
SIGNED: L.2 Atv
APPROVAL BY THESIS DIRECTOR
This thesis has been approved on the date shown below:
VsAs R (?\..) E. S. SIMPSON Date Professor of Hydrology ACKNOWLEDGMENTS
This thesis was partially funded by the U.S. Geological Survey,
Water Resources Division, Tucson, Arizona, under the Southwest Alluvial
Basins Regional Aquifer Systems Analysis Program. The author gratefully acknowledges the technical input and groundwater chemical analyses for the Ranegras Plain groundwater basin provided by Fred N. Robertson of the U.S. Geological Survey, Tucson, Arizona. Review comments and suggestions from Dr. Eugene S. Simpson, Dr. Stan N. Davis, and Dr.
Austin Long of the University of Arizona significantly improved the manuscript and were greatly appreciated. I am particularly grateful to
Dr. Eugene Simpson for his continued support during the completion of this thesis. Lastly I would like to thank Kathleen Reyes, Kathy Burns,
Ann Hill, and my wife, Christina Nereson, for their help preparing the graphics for this thesis.
111 TABLE OF CONTENTS
Page
LIST OF ILLUSTRATIONS viii
LIST OF TABLES xi
ABSTRACT xii
1. INTRODUCTION 1
Purpose and Scope of Study 1 Location and Physical Setting of Study Area 2 Climate 5 Methods of Study 5 Previous Investigations of the Geology and Hydrology of the Ranegras Plain 7 Early Studies 7 Geology 7 Hydrology 8
2. GEOLOGY 10
Summary 10 Geology of the Surrounding Mountains 11 Precambrian Metamorphic and Intrusive Rocks 11 Paleozoic Sedimentary Rocks 11 Mid-Mesozoic Volcanic and Granitic Rock 13 Late Mesozoic Clastic and Metamorphic Strata 13 Late Cretaceous Plutons 15 Mid-Tertiary Rocks 15 Mid-Late Tertiary Basalt 16 Geology of Basin Fill 16 Lower Basin Fill 21 Coarse-grained Facies 21 Fine-grained Facies 22 Upper Basin Fill 24 Quaternary Alluvium 25 Basin Shape and Depth to Bedrock 25
iv V
TABLE OF CONTENTS--Continued Page
3. HYDROLOGY 28
Surface Water Hydrology 28 Groundwater Hydrology 29 Occurrence of Groundwater 29 Regional Groundwater Movement 29 Groundwater Recharge 31 Groundwater Discharge 32 Depth to Water and Water-table Elevations 33 Well Yields 34 Specific Capacity and Transmissivity 35
4. GEOCHEMISTRY OF STRONTIUM 36
Chemical Behavior of Strontium 36 Strontium Minerals 37 Strontianite 37 Celestite 38 Factors Controlling the Formation of Strontium Minerals 38 Strontium as a Minor Constituent of Minerals 39 Igneous Rocks 39 Sedimentary Rocks 41 Strontium in Isomorphous Series 42 Occurrence of Strontium Mineral Deposits in California and Arizona 42 Strontium Hydrogeochemistry 45 Strontium Concentrations in Natural Waters 45 Geologic Conditions Accompanying High Strontium Concentrations in Ground Water 47 Celestite and Strontianite Occurrences in Glacial Till and Limestone Aquifers 47 Limestone Aquifers Undergoing the Diagenesis of Aragonite to Calcite 48 Aquifers in Contact with Evaporites and Brines 50 Previous Studies Using Strontium as a Hydrogeologic Tracer 51 Hydrogeologic Studies Using Strontium Isotope Geochemistry 51 vi
TABLE OF CONTENTS--Continued
Page
5. HYDROGEOCHEMISTRY OF THE RANEGRAS PLAIN BASIN 56
Summary 56 Source and Analysis of Groundwater Quality Data 57 General Mineral Hydrochemistry 62 Total Dissolved Solids 62 Relationship of Well Depth and Water Quality 64 Water Type 64 pH 67 Sodium 67 Calcium 70 Magnesium 70 Potassium 73 Chloride 73 Sulfate 76 Bicarbonate and Carbonate 78 Fluoride 80 Groundwater Recharge 82 Mineral Saturation Indices 83 Weathering of Silicate Minerals 86 Dissolution of Evaporites 92 Cation Exchange 93
6. STRONTIUM HYDROCHEMISTRY OF THE RANEGRAS PLAIN BASIN 99
Summary 99 Occurrence and Distribution of Strontium in Groundwater . 100 Correlation of Strontium with Other Dissolved Constituents in Ground Water 102 Mechanisms Controlling the Strontium Concentrations in Groundwater 106 Dissolution of Celestite and Strontianite 108 Release of Strontium During the Weathering of Silicate Minerals 111 Solid Solution of Strontium in Calcite, Aragonite, and Gypsum 113 Solid Solution of Strontium in Calcite 113 Calcite Sources 113 Calcite Saturation 114 Calcium Concentrations Calculated from the Model CaCO3 -H2O-0O2 Plus Acid or Base 117 Solid Solution of Strontium in Gypsum 124 vii
TABLE OF CONTENTS--Continued
Page
Solid Solution Calculations 126 Published Values of Partition Coefficients 127 Control of Strontium Concentrations by Equilibrium with Aragonite and Strontianite . 129 Calculation of Sr/Ca Ratios for Calcite, Aragonite, and Gypsum in the Ranegras Plain 131 Cation Exchange 133 Strontium Adsorption on Clays 134 Ion Exchange Equilibria 135 Strontium Adsorption on Sesquioxides 138 pH Dependence of Adsorption on Clays 138 Effect of High Strontium Concentrations on Strontium Adsorption 139 Estimate of Adsorbed Strontium on Montmorillonite at the Ranegras Plain Basin 139
7. ANALYSIS OF POTENTIAL STRONTIUM SOURCE ROCKS AND WELL CUTTINGS 145
Analysis of Source Rocks 145 Analysis of Well Cuttings 150 Well No. 7 151 Well No. 64 155 Strontium in the Sediments of Closed Lake Basins 156 Solid Solution Calculations for Well No. 7 158 Summary 160
8. CONCLUSIONS 162
APPENDIX A: WELL LOGS 167
APPENDIX B: SCATTERGRAMS 173
APPENDIX C: ANALYTICAL PROCEDURES FOR THE ANALYSIS OF STRONTIUM, CALCIUM, AND SULFATE IN ROCK SAMPLES AND WELL CUTTINGS 180
REFERENCES: 186 LIST OF ILLUSTRATIONS
Figure Page
1. Location of study area 3
2. Physiographic features of the Ranegras Plain basin 4
3. Geologic map of the Ranegras Plain basin 12
4. Locations of geologic cross sections and lateral extent of the fine-grained facies 18
5. Geologic cross section A-A' 19
6. Geologic cross section B-B' 20
7. Depth to bedrock in basin alluvium 27
8. Water-level elevation map 30
9. Well location map 61
10. Total dissolved solids concentrations in groundwater 63
11. Stiff diagram map 66
12. pH of groundwater 68
13. Sodium concentrations in groundwater 69
14. Calcium concentrations in groundwater 71
15. Magnesium concentrations in groundwater 72
16. Potassium concentrations in groundwater 74
17. Chloride concentrations in groundwater 75
18. Sulfate concentrations in groundwater 77
19. Bicarbonate concentrations in groundwater 79
viii ix
LIST OF ILLUSTRATIONS--Continued
Figure Page
20. Fluoride concentrations in groundwater 81
21. Log [Na]/[H] versus log [H4SiO4 ] 88
22. Log [Ca 2± ]/[1-01 2 versus log [H4 SiO4 ] 88
23. Log [Ca 24 ]/[114 ] 2 versus log [Na]/[H] 89
24. Log [Ca 24 ]/[e] 2 versus log [e]/[11+ ] 89
25. Log [Mg 2-1 ]/[e] 2 versus log [e]/[e] 90
26. Strontium concentrations in groundwater 101
27. Histogram of strontium concentrations in groundwater samples from wells in the Ranegras Plain basin 103
28. Cumulative frequency distribution of strontium activity in groundwater 104
29. Strontium concentrations in groundwater versus pH 107
30. Strontium concentration in groundwater versus strontianite saturation index 110
31. Strontium concentration in groundwater versus celestite saturation index 110
32. Saturation of groundwater with respect to calcite 115
33. Strontium concentrations in groundwater versus calcite saturation index 118
34. Strontianite saturation index versus calcite saturation index 118
35. Calcite saturation index versus pH of groundwater 119
36. Log activity calcium versus pH 122
37. Strontium concentration in groundwater versus gypsum saturation index 125
38. Gypsum saturation index versus calcite saturation index . . 125 LIST OF ILLUSTRATIONS--Continued
Figure Page
39. Location of strontium source rock samples and well cutting samples 147
40. Strontium concentrations and Sr/Ca molar ratios of the acid-extractable fraction of well cutting samples from Well No. 7 as a function of depth 154
B-1 Scattergram of strontium versus calcium 174
B-2 Scattergram of strontium versus magnesium 174
B - 3 Scattergram of strontium versus sodium 175
B-4 Scattergram of strontium versus potassium 175
B-5 Scattergram of strontium versus sulfate 176
B-6 Scattergram of strontium versus chloride 176
B-7 Scattergram of strontium versus bicarbonate 177
B-8 Scattergram of strontium versus carbonate 177
B-9 Scattergram of strontium versus fluoride 178
B-10 Scattergram of strontium versus silica 178
8-11 Scattergram of strontium versus total dissolved solids . . . 179 LIST OF TABLES
Table Page
1. Chemical analyses of groundwater samples 59
2. Well construction details 60
3. Major ion content of groundwater 65
4. Mineral saturation indices 84
5. Comparison of chemical analyses of groundwater samples from Wells No. 15 and 16 94
6. Comparison of chemical analyses of groundwater samples from Wells No. 35 and 36 96
7. Correlation coefficients of strontium with other dissolved constituents and physical and chemical parameters 105
8. Comparison of observed and calculated Sr/Ca molar ratios in calcite, aragonite, and gypsum based on the solid solution of strontium 132
9. Calculation of adsorbed strontium on montmorillonite clay . . 142
10. Chemical analyses of potential strontium source rocks . . . 148
11. Chemical analyses of well cuttings samples 152
12. Calculated Sr/Ca ratios for well cuttings from Well No. 7 assuming solid solution of strontium with calcite, aragonite, and gypsum 159
C-1. Operating conditions for atomic adsorption Spectrophotometric analysis of calcium and strontium 184
xi ABSTRACT
The occurrence, sources, and governing geochemical reactions of strontium in the groundwater of the Ranegras Plain basin, western Ari- zona, were evaluated by the analysis of basin geology, groundwater quality data, and chemical analyses of basin drill cuttings and poten- tial strontium source rocks from the surrounding mountains. Four potential mechanisms controlling the hydrogeochemistry of strontium were evaluated: (1) celestite and strontianite dissolution; (2) strontium release during the weathering of silicate minerals; (3) the solid solu- tion of strontium in calcite, aragonite, and gypsum; and (4) cation exchange.
Evaporite dissolution, aluminosilicate mineral hydrolysis, calcite precipitation, and cation exchange control the basin hydrogeo- chemistry. Strontium concentrations in groundwater range from 0.060 to
4.4 milligrams per liter and are controlled primarily by pH, gypsum dissolution and calcite precipitation of which strontium is a trace component, and the cation exchange of strontium on aquifer minerals.
xi i CHAPTER 1
INTRODUCTION
Purpose and Scope of Study
The purpose of this study was to assess the occurrence, sources,
and geochemical controls of naturally occurring strontium in the ground-
water of the Ranegras Plain groundwater basin, an alluvial basin in
west-central Arizona. Strontium concentrations range up to 4.4 mg/1 in
the groundwater of this basin.
The major ion hydrogeochemistry of the basin was characterized
by evaluation of chemical analyses of groundwater samples, correlation with basin geology and hydrology, and geochemical calculations.
This thesis includes a review of the hydrology of the Ranegras
Plain basin, the geology of the surrounding mountains, and the geochem-
istry of strontium with emphasis on studies of strontium in groundwater.
Geologic cross-sections of the basin sediments were prepared to charac-
terize the basin sediments contributing to the aqueous geochemistry of
strontium.
Four geochemical mechanisms potentially controlling the concen-
tration of strontium in groundwater were evaluated: (1) dissolution of
strontianite and celestite, (2) the release of strontium during the weathering of silicate minerals, (3) the solid solution of strontium in gypsum and calcite, and (4) cation exchange.
1 2
Potential sources of the elevated concentrations of strontium in the Ranegras Plain were evaluated by the chemical analysis of rock samples from the mountains surrounding the basin and of well cuttings samples from boreholes within the basin sediments.
Location and Physical Setting of Study Area
The Ranegras Plain is an arid alluvial basin in west-central
Arizona approximately 100 miles west of Phoenix, Arizona, and 40 miles east of Blythe, California (Figure 1). The basin is in La Paz County,
Arizona, formerly the northern half of Yuma County, Arizona. This northwest-trending basin is contained in the Basin and Range Lowlands physiographic province (Fenneman, 1931), and is approximately 50 miles long by 15 miles wide. It is bounded on the east by the Granite Wash
Mountains, Little Harquahala Mountains, Black Rock Hills, and Cemetery
Ridge, on the north by the Bouse Hills, on the west by the Plomosa Moun- tains, Bear Hills, and New Water Mountains, and on the south and south- west by the Little Horn Mountains (Figure 2). The valley floor slopes smoothly northwestward from an elevation of 1,360 feet in the southeast corner of the basin to 930 feet at the town of Bouse in the northwest corner of the basin. Bouse is the largest settlement in the area.
Bouse Wash, an ephemeral tributary of the Colorado River, drains the basin.
The sparse vegetation on the desert floor consists primarily of creosote bush and salt grass. Higher elevations in the surrounding mountains support growth of palo verde trees, greasewood, ocotillo, and abundant cactus dominated by saguaro, cholla, and prickly pear. 3
• KINGMAN • FLAGSTAFF
• PRESCOTT
0 Tr RANEGRAS PLAIN BASIN cc 0 • PHOENIX • GLOBE QUARTZITE
YUMA
• TUCSON
0 25 50 MILES
0 25 50 75 KILOMETRES
Figure 1. Location of study area. 4
Figure 2. Physiographic features of the Ranegras Plain basin. 5
Climate
Hot, dry summers alternating with mild winters characterize the
arid climate of the Ranegras Plain. The mean annual precipitation at
the town of Bouse for the period of 1953 through 1970 was only 5.06
inches (Sellers and Hill, 1974). Thirty percent of the yearly rainfall
occurs during the wettest months of July and August. During this time,
afternoon thunderstorms characterized by high rainfall intensity and
rapid runoff are produced as moist air from the Gulf of Mexico is forced
upward by mountains and heat-driven thermals. Heavy late summer rains,
occurring every few years, are associated with tropical storms from the
Pacific Ocean.
The remainder of the yearly rainfall occurs fairly evenly over
the period of September to April. May and June receive only trace amounts of rainfall. Winter storms from the north Pacific produce gentle rains that last for days and generate little runoff.
Average summer daily temperatures exceed 90°F (32°C), with after- noon highs frequently above 110°F (43°C). Average winter temperatures are 50 ° F (10°F), with afternoon readings from 75 to 80°F (24 to 27°C).
Methods of Study
This thesis includes generalized geologic cross sections of the
Ranegras Plain basin prepared from available well logs to characterize the subsurface geology and to correlate the geology with groundwater chemistry.
The author assessed the major ion and strontium hydrogeochem- istry of the Ranegras Plain groundwater basin by the preparation of 6 water quality maps, the evaluation of mineral saturation indices and mineral stability diagrams, statistical correlations of dissolved ground- water constituent concentrations, and geochemical equilibrium calcula- tions. Chemical analyses of groundwater provided by the U.S. Geological
Survey were analyzed by the WATEQF geochemical speciation program
(Plummer, Jones, and Truesdale, 1976) to calculate equilibrium concen- trations of hydrochemical species and mineral saturation indices. Sta- tistical correlations and scattergrams of the concentrations of stron- tium and selected dissolved chemical species were completed with the
SPSS computer program (Nie et al., 1975).
The author analyzed drill cuttings of basin sediments and rock samples from the surrounding mountains to evaluate sources of the high strontium concentrations in groundwater and to correlate basin sediment mineralogy with water chemistry.
The control of basin hydrogeochemistry by calcite saturation was evaluated by the comparison of groundwater samples to the model CaCO 3 -
H2 O-0O 2 . The author calculated strontium/calcium molar ratios for cal- cite, aragonite, and gypsum, based on the solid solution of strontium in these minerals and available chemical analyses of groundwater, and com- pared the calculated ratios to literature values and those measured in sediment samples from the Ranegras Plain basin. The author calculated the concentration of strontium adsorbed to clays in the basin based on specific assumptions and compared these concentrations to literature values. 7
Previous Investigations of the Geology and Hydrology of the Ranegras Plain
Early Studies
Reconnaissance geological surveys of Yuma County, published during the first quarter of this century, provided physiographic maps, documented known mineral and water resources, and briefly described the major lithologic units (Lee, 1908; Bancroft, 1911; Jones, 1916; Ross,
1922, 1923; Darton, 1925). Ross (1922) published the first complete description of the general geology of western Arizona. Ross (1923) described the hydrology and topography of western Arizona and provided a reconnaissance geologic map of the area.
Geology
Metzger (1951) discussed the groundwater resources and geology of the northern part of the Ranegras Plain. Included in his report are the first detailed geologic map of the area and discussion of the geol- ogy of the surrounding mountains and basin fill.
Wilson (1960) published the first geologic map of Yuma County.
This map remained unchanged on the state geologic map (Wilson, Moore, and Cooper, 1969). Detailed studies of the surrounding mountain chains were completed in the 1960's: northern Plomosa Mountains (Jemmett,
1966), Granite Wash Mountains (Ciancanelli, 1965), and southern Plomosa
Mountains, New Water Mountains, and Livingston Hills (Miller and McKee,
1971). The area mapped by Miller (1966) was revised and published as the Geologic Map of the Quartzite Quadrangle, Yuma County, Arizona
(Miller, 1970). Harding (1978, 1980) discussed the petrology and 8 tectonic setting of the Livingston Hills Formation in the Livingston
Hills. Robinson (1979, 1980) studied outcrops of Mesozoic continental red-bed deposits in the southernmost Plomosa Mountains. Marshak (1979) reported on the geology of Mesozoic sedimentary rocks in the Dome Rock
Mountains, Little Harquahala Mountains, Granite Wash Mountains, Plomosa
Mountains, and Buckskin Mountains. Additional detail on the geology of the Plomosa Mountains was presented by Scarborough and Wilt (1979) in their study of uranium favorability of Cenozoic sedimentary rocks.
Scarborough and Pierce (1978) described the geology of late Cenozoic basins in Arizona. Eberly and Stanley (1978) covered Cenozoic strati- graphy and complied K-Ar age data for southwestern Arizona. A compre- hensive K-Ar geochronology and geologic history of southwestern Arizona is presented by Shafiqullah et al. (1980). Reynolds (1980) provided a complete summary of geology in west-central Arizona including the Rane- gras Plain Basin. Detailed descriptions of Mesozoic structures in the
Granite Wash and Plomosa Mountains are provided by Reynolds et al.
(1986). Reynolds (1988) published an updated Arizona state geologic map that includes recent geologic mapping in the mountains surrounding the
Ranegras Plain basin.
Hydrology
Metzger (1951) completed the first detailed study of groundwater resources in the Ranegras Plain, and included a discussion of the occur- rence and movement of groundwater, recharge, discharge, and safe yield, as well as a basic data compilation of driller's logs, well records, and water analyses. Briggs (1969) documented the change of groundwater 9 conditions between 1948 and 1967 by the use of depth-to-water maps and an expanded basic well data compilation. Wilkins and Webb (1976) published updated maps showing depth-to-water, well depths, water-level elevations, specific conductance and fluoride concentrations in ground- water, irrigated acreage in 1974, and change in water levels from 1967 to 1975. Winograd and Robertson (1982) used well water analyses from the Ranegras Plain to document the presence of dissolved oxygen in deep well waters. Robertson (1985) discussed the occurrence and solubility of fluoride and barium of groundwater in the Ranegras Plain. CHAPTER 2
GEOLOGY
Summary
The geology of the Ranegras Plain and surrounding mountains is complex and includes many geologic units. The basement of Precambrian granite and gneiss are unconformably overlain by a sequence of Paleozoic carbonate and clastic rocks. Mesozoic rocks are represented by interme- diate to felsic volcanic and plutonic rocks, which are overlain by a thick sequence of clastic rocks. The Mesozoic sediments were regionally metamorphosed in large areas during the Cretaceous-Tertiary and intruded by Laramide plutons. Mid-Tertiary sections are composed of clastic rocks and volcanics of primarily andesitic composition. Large volumes of late-Tertiary basalt were extruded prior to and synchronous with late
Miocene basin-and-range block faulting, which created the present Rane- gras Plain basin. The present basin boundaries are the result of the widening of the late Miocene basin boundary due to erosion of the sur- rounding mountain blocks and sediment deposition in the basin bottom
(Scarborough and Peirce, 1978). The basin fill, which exceeds 1,600 feet in depth at the basin center, is composed of a coarse-grained pied- mont facies at the basin perimeter, and a fine-grained lacustrine or playa facies in the basin center.
10 1 1
Geology of Surrounding Mountains
This section discusses the geology of the mountains surrounding the Ranegras Plain under the following general categories of rock types defined by Reynolds (1980) and shown on the generalized geologic map,
(Figure 3): Precambrian metamorphic and intrusive rocks, Paleozoic sedimentary rocks, Mid-Mesozoic volcanic and granitic rocks, Late Meso- zoic clastic and metamorphic strata, Late Cretaceous plutons, Mid-
Tertiary rocks, and Mid-late Tertiary basalt.
Precambrian Metamorphic and Intrusive Rocks
Outcrops of Precambrian granite are present in the eastern
Little Harquahala Mountains, the Black Rock Hills, and the western Plo- mosa Mountains south of I-10 (Reynolds, 1980). This medium- to coarse- grained granite is composed of quartz, feldspar, and chlorite (Marshak,
1979). Small exposures of Precambrian gneiss are found on the eastern flank of the Plomosa Mountains, just west of Bouse (Jemmett, 1966).
Paleozoic Sedimentary Rocks
Isolated patches of Paleozoic sedimentary rocks outcrop in the eastern Little Harquahala Mountains, western Granite Wash Mountains, and southern Plomosa Mountains. These strata consist of interbedded lime- stone, dolomite, quartzite, and siltstone (Reynolds, 1980). The forma- tions present in this sequence include the Boisa Quartzite (Cambrian), the Abrigo Formation (Cambrian), the Martin Formation (Devonian), the
Escabrosa Limestone (Mississippian), the Supai Formation (Pennsylvanian-
Permian), the Coconino Sandstone (Permian), and the Permian Kaibab 12
EXPLANATION
MAP UNITS
0 Surficial Deposits Jay Sedimentary and Volcanic Rocks (Holocene to Middle Pleistocene) (Jurassic)
Qo Older Surficial Deposits Jv Volcanic Rocks (middle Pleistocene to latest Pliocene) (Jurassic)
Tsy Sedimentary Rocks MzPz Mesozoic and Paleozoic Rocks (Pliocene to Middle Miocene) -Structurally Complex Jurassic, Triassic, and Paleozoic Rocks Tb Basaltic Rocks (late to middle Miocene) Pz Paleozoic Sedimentary Rocks
...i.nommoomr Tsm Sedimentary Rocks 7 Yg Granitoid Rocks (middle Miocene to Oligocene) (Middle Proterozoic)
Tv Volcanic Rocks Xg Granitiod Rocks (middle Miocene to Oligocene) (Early Proterozoic)
Tsv Volcanic and Sedimentary Rocks Xm Metamorphic Rocks (middle Miocene to Oligocene) (Early Proterozoic)
=11 Tg Granitoid Rocks Xmv Metavoicanic Rocks * %, »»:•2 _ (early Miocene to Oligocene) (Early Proterozoic)
" < Tkg Granitoid Rocks (early Tertiary to Late Cretaceous) MAP SYSMBOLS Kjs Sedimentary Rocks With Local Volcanic Units (Cretaceous to Late Jurassic) Contact + + + • jg Granitoid Rocks +++ (Jurassic)-Granite to Diorite, with Fault Local Alkaline Rocks
Source: Reynolds (1988)
0 5
SCALE IN MILES
Figure 3. Geologic map of the Ranegras Plain basin. 13
Formation (Harding, 1978; Miller, 1970; McKee, 1951; Wilson, 1962; Rey- nolds, 1980).
The Paleozoic sequence in the Plomosa Mountains near the Bouse-
Quartzite Road and on the western flank of the Granite Wash Mountains has been moderately to highly metamorphosed and consists of interbedded quartzite, marble, and siliceous carbonate rock (Ciancanelli, 1965;
Miller, 1966; Marshak, 1979; Reynolds et al., 1986).
Mid-Mesozoic Volcanic and Granitic Rock
Volcanics of probable mid-Mesozoic age occur in the Little Har- quahala and southern Plomosa Mountains (Miller, 1970; Marshak, 1979;
Harding, 1978; Reynolds, 1980). Composition ranges from dacite to rhyo- lite, and the rocks occur as flows, ash-flow tuffs, and coarse agglomer- ate, locally interbedded with volcanic conglomerates, sandstone, mud- stone, and other clastic rocks (Reynolds, 1980). Granitic plutons that appear roughly synchronous with the volcanics occur in the southern
Plomosa and northern Kofa Mountains.
Late Mesozoic Clastic and Metamorphic Strata
An extremely thick sequence, up to 16,000 feet, of predominantly clastic sedimentary rocks is widely distributed throughout northern Yuma
County and constitutes the primary rock type in the northern and south- ern Plomosa Mountains and the western Granite Wash Mountains (Wilson,
1962; Miller, 1966, 1970; Jemmett, 1966; Harding, 1978; Marshak, 1979;
Robinson, 1979; Reynolds, 1980, Reynolds et al., 1986). Other exposures occur in the Little Harquahala Mountains, Blackfoot Hills and Cemetery 14
Ridge. Miller (1970) informally named the lower Mesozoic clastic se- quence as continental red-bed deposits, and formally defined the upper
Mesozoic sequence as the Livingston Hills Formation.
The "Red Beds" consist of an interbedded and mixed assemblage of coarse- to fine-grained clastic and finely crystalline carbonate rock composed of 40 percent mudstones, 25 percent sandstones, 15 percent siltstone, 15 percent carbonates, and 5 percent conglomerate (Robinson,
1979). Some calcareous strata are rich in gypsum. The "Red Beds" in the southern Plomosa Mountains were correlated with Mesozoic strata in the Granite Wash and Little Harquahala Mountains (Robinson, 1979; Mar- shak, 1979).
The Livingston Hills Formation conformably overlies the "Red
Beds" and is approximately 12,000 feet thick. It consists of an exten- sive sequence of conglomerate, graywacke, and siltstone (Miller, 1970;
Harding, 1978).
In the northern Plomosa Mountains, the Mesozoic strata have been metamorphosed to quartzite, marble, phyllite, schist, and gneiss (Wil- son, 1962; Jemmett, 1966; Marshak, 1979; Reynolds, 1980; Reynolds et al., 1986). The late Mesozoic clastic strata in the Granite Wash Moun- tains are relatively unmetamorphosed in the westernmost outcrops (sub- greenschist grade), but are progressively metamorphosed and deformed to the east into phyllite, schist, and gneiss (amphibolite grades)
(Ciancanelli, 1965; Marshak, 1979; Reynolds, 1980). This regional meta- morphism of Mesozoic rocks is due to a period of Cretaceous-Tertiary regional deformation and metamorphism, which also affected precambrian 15
rocks, Paleozoic strata, and mid-Mesozoic volcanics (Reynolds, 1980;
Reynolds et al., 1986).
Late Cretaceous Plutons
Late Cretaceous Laramide plutons are exposed in the Bouse Hills,
Granite Wash Mountains, and the Little Harquahala Mountains. Rock com-
position varies from diorite to granite. The Granite Wash Mountains are underlain by two separate plutons, the Tank Pass granite and the Granite
Wash granodiorite. The Tank Pass granite occurs in the northeastern
quarter of the range and is intruded by the Granite Wash granodiorite.
Both plutons were dated by K-Ar and Rb-Sr isotope analysis (Shafiqullah
et al., 1980; Reynolds, 1980).
Mid-Tertiary Rocks
Mid-Tertiary rocks are dominated by volcanics of primarily ande-
sitic composition, which occur abundantly in the central Plomosa Moun-
tains, Bouse Hills, New Water Mountains, Kofa Mountains, Eagletail
Mountains, and Black Rock Hills. These rocks consist of dark-colored
flows, flow breccia, and minor cemented ash and cinder deposits of ande-
sitic to basaltic-andesitic composition. Although these volcanics are
shown as Cretaceous on the state geologic map (Wilson et al., 1969) and
the Yuma County geologic map (Wilson, 1980), K-Ar age dates ranging from
25 to 15 million years before present [m.y.B.P.] (Eberly and Stanley,
1978; Shafiqullah et al., 1980), indicate that they are probably all mid-Tertiary. Intrusive equivalents of these rocks occur as dikes or plugs in the northern Kofa Mountains and the Eagletail Mountains. 16
Mid-Tertiary sedimentary rocks on the eastern flank of the north- ern Plomosa Mountains occur as rotated fault blocks consisting of a basal arkosic conglomerate, overlain by greater than 200 feet of thinly- bedded calcareous slabs and limestone, overlain by several hundred feet of andesitic flow breccia with welded rhyolite capping. The unit listed as TKs on the state geologic map (Wilson et al., 1969) is a series of dark red-brown mudflow-rich fanglomerates with abundant clasts of Pre- cambrian and Mesozoic metamorphic rocks (Jemmett, 1966; Scarborough and
Wilt, 1979).
Mid-Late Tertiary Basalt
Large volumes of middle to late Tertiary basalt occur in the New
Water Mountains, Bear Hills, Kofa Mountains, Little Horn Mountains, and
Cemetery Ridge, and as a line of isolated hills west of the Little Har- quahala Mountains. The thin dark-gray olivine basalt flows are commonly vesicular (Metzger, 1951; Reynolds, 1980). These rocks, listed on the state geologic map as Quaternary (Wilson et al., 1969), have since been shown to be Miocene by K-Ar age dates and stratigraphic relations (Shaf- iqullah et al., 1980; Eberly and Stanley, 1978). This period of volcan- ism continued into the late Miocene block-faulting episode, as shown by the occasional presence of interbedded basalt flows and ash-fall tuffs in the Tertiary basin fill.
Geology of Basin Fill
Basin fill, as defined by Scarborough and Peirce (1978), is the sedimentary group that was deposited in the basins created by the basin- 17 and-range disturbance. This late Miocene block faulting episode created the "typical basin-and-range structure of mountain-forming horsts separ- ated by valleys underlain by grabens" (Eberly and Stanley, 1978). These subsiding fault-bound basins became depositional centers for clastic material from adjacent highlands and for evaporites and minor volcanics.
The main episode of deposition accompanied late Miocene block faulting from 14 to 5 m.y.B.P., but deposition has continued up to the present
(Eberly and Stanley, 1978; Scarborough and Peirce, 1978; Reynolds 1980).
The Ranegras Plain basin fill consists predominantly of late
Tertiary fanglomerate, poorly- to moderately-consolidated sand, silt, clay, and gravel, occasional interbedded volcanic flows or tuffs, and minor amounts of evaporites (Metzger, 1951; Eberly and Stanley, 1978;
Scarborough and Peirce, 1978). Total thickness of the basin fill exceeds 1,600 feet.
Stratigraphic correlation of 42 driller's logs and two litho- logic logs was used to divide the Ranegras Plain basin fill into two separate geologic units defined as upper basin fill and lower basin fill. Lower basin fill represents sediment deposited in the actively subsiding basin from the mid-Miocene to probably mid-Pliocene. The upper basin fill overlies the lower basin fill and represents younger sediments that are unfaulted at the basin margins and rest upon the erosional surface of down-faulted mountain blocks (Scarborough and
Peirce, 1978). Figures 5 and 6 represent longitudinal and lateral geologic cross sections of the Ranegras Plain basin. The locations of the geologic cross sections are shown on Figure 4. 18
A 7)23ca
B (5-17)2445
B(5-15
8(5 110355:102 B(5-115)3410c0
BC -15)7obb 0\ ( 4 -i5)l s14.bb 1 4-15)15bcc,— • • W4-15)2404: \ B( 4-14 19ba• 1- \
APPROXIMATE LATERAL EXTENT 0 5 OF FINE-GRAINED FACES =TTC A A . OF THE LOWER BASIN FILL SCALE IN MILES GEOLOGIC CROSS-SECTION
Figure 4. Locations of geologic cross sections and lateral extent of the fine-grained facies of the lower basin fill. 19
O O
013 0 01(PL -Z)E3
qspe(g I. 8)9
qqqs t. cs t—s98
00PS Z(9 I. -9)9
80P0 I. (9 1-9) 9
BeeCE(9 1-9)9
ciPPZ(L I. -9)8
130£3(/ L -L)8 I I I I I I I o o o o o o o O o o o o o o O o co co nt cm o, .- 1 CTS'IrA ) NOLLVA313 20
EAST WEST B'
1200
100o- FINE-GRAINED FACIES OF LBF
800 -
600 -
400 - COARSE-GRAINED FACIES OF LBF 200 -
0 -
-200 -
-400
-600 0 4M1.
HORIZONTAL SCALE
EXPLANATION
UBF - UPPER BASIN FILL LBF - LOWER BASIN FILL ESTIMATED DEPTH TO BEDROCK BASED ON GRAVITY MODELLING (OPPENHEIMER AND SUMNER, 1980)
Figure 6. Geologic cross section B-B'. 21
Lower Basin Fill
Lower basin fill represents sediment deposited in the actively subsiding basin from the mid-Miocene to probably mid-Pliocene. Total depth determined from well logs exceeds 1,200 feet. This late Tertiary basin fill was deposited into a closed drainage and is composed of a coarse-grained facies at the base and perimeter of the basin, and a fine-grained valley-center facies. The lateral extent of the fine- grained facies is shown on Figure 4.
Coarse-grained Facies. The coarse-grained facies, also known as fanglomerate or piedmont facies, is composed of "bedded cobble conglom- erate" with "lenses and channel-fill pods of fluvial sand and unsorted, unbedded debris flows" (Scarborough and Peirce, 1978). Driller's logs report "gravel, rock, sandstone, conglomerate, sand and gravel, clay and gravel, and rock and conglomerate" (U.S. Geological Survey, 1983).
Almost every well in the east side of the basin is perforated in the coarse-grained facies of the lower basin fill (T. 4 N., R. 14 W.; the northeast quarter of T. 4 N., R. 15 W.; and the eastern half of
T. 5 N., R. 15 W.) [Figure 4]. These wells are located just west of the line of volcanic hills containing Pyramid Peak. The bottom of the bore- holes used to complete these wells encountered volcanic rock described as "malapai, cemented lava, and volcanic formation" in driller's logs
(U.S. Geological Survey, 1983). The volcanics probably represent the top of a down-faulted block on the eastern basin margin, and not inter- bedded flows in the basin fill, since thick volcanic sequences are not found in the fine-grained facies. The volcanics occur at a depth of 700 22
to 900 feet below the land surface [elevation 130 to 760 feet above sea
level (f.a.s.1.)] and at shallower depths in the more easterly wells,
thus suggesting en echelon faulting on the eastern basin boundary. The bottom 300 feet of well B(5-15)18DDA intersects volcanic rock, demon-
strating that the volcanics are at least 300 feet thick in that area.
Red "malapai" is also reported on the west side of the basin in well B(4-16)18DCB below a depth of 120 feet. This small alluvial area west of the Bear Hills may be considered a separate basin. Volcanics
are not reported in well logs for other parts of the basin; however, wells on the west side of the basin may intersect volcanics if they were
sufficiently close to the basin boundary.
The coarse-grained facies is less than one mile wide in many areas on the east side of the basin (Figure 4). Well B(4-15)24BAA, which is drilled into the fine-grained facies, intersects 200 feet of sandy clay and 300 feet of sticky clay, whereas wells B(4-15)13BDA and
B(4-14)19BAA, located 0.7 mile north and 1.0 mile east, respectively,
intersect all coarse sediment.
Wells in the basin center that are sufficiently deep (600 to
1200 feet below ground surface) pass through the fine-grained facies and intersect the underlying coarse-grained facies [e.g. Well B(4-15)18BBC].
Fine-grained Facies. The fine-grained facies in the interior of the basin consists primarily of clay with minor amounts of sand and silt, and occasional interbedded layers of sand or gravel with minor gypsum. Driller's logs report "sandy clay; white, yellow, or brown clay; clay-gravel; or clay with some fine sand" (U.S. Geological Survey, 23
1983). The fine-grained facies consists of fluvial overbank and lacus-
trine sediments deposited under oxidizing conditions and is character-
ized by clay and sandy clay containing local gypsum beds and air-fall ash beds. The environment of deposition is summarized as "a series of
local shallow playas or salt lake basins separated by large fan deposits" (Davis and Brooks, 1930).
Only one lithologic log is available for wells drilled in the fine-grained facies, Well B(3-15)2DAB (Appendix A). Unfortunately, the well cuttings were washed prior to analysis, so the particle size analy- sis is not accurate. The sand and gravel fractions consist of approxi- mately 40 to 45 percent volcanics, 1 to 20 percent sandstone, and occasional fragments of limestone. The volcanic fragments are mostly andesite above 300 feet depth and predominantly rhyolite and welded tuff below 300 feet depth. The presence of gypsum in the fine-grained facies implies internal (closed) drainage in the Ranegras Plan Basin during the mid-Miocene to mid-Pliocene. Gypsum occurs between 700 and 920 feet depth in the amount of 1 to 5 percent. This zone also has a much higher percentage of fine-grained sediment (50 to 74 percent) than the under- lying and overlying intervals. A pyrite fragment was found at a depth of 840 feet.
White sticky clay beds, most likely bentonite, are found in both the fine- and coarse-grained facies on the east side of the basin at depths of 500 to 700 feet below land surface (elevation 500 to 750 f.a.s.1.). The thickness of the clay beds range from 10 to 50 feet and averages 20 feet. Bentonite is formed by the weathering of volcanic ash 24
to produce primarily smectite clays that are colloidal and plastic
(Blatt, Middleton, and Murray, 1980).
Metzger (1951) reported a clay deposit approximately one mile
southeast of Bouse, which he interpreted as having been formed in a
recent playa. A few hundred tons of bentonite were mined east of Bouse
for local use as drilling mud (ABM Bull. 180, 1969; Keith, 1978). These
deposits are probably not part of the upper basin fill, because benton-
ite is formed by the alteration of volcanic ash or tuff, and no volcan-
ism is known to have occurred during the deposition of the upper basin
fill.
Upper Basin Fill
Upper basin fill overlies the lower basin fill and represents
younger sediments that are unfaulted at the basin margins and rest upon
the erosional surface of down-faulted mountain blocks (Scarborough and
Peirce, 1978). Upper basin fill was deposited during the approximate
period late Pliocene to mid-Pleistocene. The change in depositional
environment can be attributed to the decreased level of basin faulting,
and the transition from internal drainage to the external integrated
drainage with the Colorado River. Lucchita (1972) concluded that the period of internal drainage continued until the development of the Colo-
rado River drainage between 10 and 3.3 m.y.B.P., but probably after 5.4 m.y.B.P.
Upper basin fill consists of 150 feet to 200 feet of sandy clay or silty clay with minor amounts of gravel. These sediments generally are finer-grained than the coarse-grained facies of the lower basin 25 fill, and contain a larger percentage of sand or silt that the fine- grained facies of the lower basin fill. The upper basin fill is common- ly cemented by caliche. The upper basin fill is coarser-grained at the basin perimeter than in the basin center. The contact between the lower basin fill and upper basin fill is difficult to distinguish in the southern half of the basin.
Quaternary Alluvium
The youngest Quaternary alluvium consists of the coarse, unsorted, and unconsolidated sand and gravel in Bouse Wash, Cunningham
Washington, and the numerous tributary washes originating in the sur- rounding mountains.
Bouse Wash has a well-defined channel in the northern third of the basin, but is poorly defined and up to one mile wide in the southern half of the basin. Ross (1923) reported that the road from Vicksburg to
Quartzite crossed an area of "extensive adobe flat" between Desert Well and the Bear Hills. "In time of flood, layers of fine silt are spread out over the flats, which are soon dried out by the sun."
Basin Shape and Depth to Bedrock
The Ranegras Plain basin trends northwest, the result of a northeast directed extensional field during the late Miocene (Reynolds,
1980). The basin margins were originally determined by steep normal faults caused by the basin-and-range disturbance, but the area of the basin has since been enlarged by erosion and pedimentation of the sur- rounding uplifted mountain blocks. 26
Pediments occur on granitic rock in the southeast and east bor- der of the Bouse Hills, and are well developed on metamorphosed sedimen- tary rocks along the southwestern border of the Granite Wash Mountains and northwest of Ibex Peak in the Plomosa Mountains (Metzger, 1951).
Depth to bedrock in the valley fill determined by gravity model- ing (Oppenheimer and Sumner, 1980) is shown in Figure 7. Control on the contour lines is greatest close to the transect lines where the gravity measurements were taken. Oppenheimer and Sumner interpreted the data to show the existence of two separate sub-basins, a relatively small one in the northwest corner of Ranegras Plain, and a second larger and deeper basin occupying the southern half of the basin. No further data sub- stantiate this interpretation, but it is not in conflict with available driller's logs. A second likely interpretation is that the two sub- basins are connected by a relatively narrow trough of depth greater than
1,600 feet. The postulated depth to bedrock of greater than 3,000 feet in the southern corner of the basin is based on one gravity measurement in that part of the basin, and, therefore, would require more detailed study to verify its existence. The depth to bedrock estimated by
Oppenheimer and Sumner (1980) is shown on cross section B-B' (Figure 6). 27
oin!0==1 SCALE IN MILES EXPLANATION Depth to bedrock was estimated by gravity modeling. 19-2-19 2 transect line -800-depth to bedrock (feet) SOURCE: Oppenheimer and Sumner, 1980.
Figure 7. Depth to bedrock in basin alluvium. CHAPTER 3
HYDROLOGY
Surface Water Hydrology
The Ranegras Plain is drained primarily by Bouse Wash, an ephem- eral tributary of the Colorado River. Included in the Bouse Wash drain- age are Butler Valley, the extreme western part of McMullen Valley, and the Ranegras Plain (Figure 2).
Cunningham Wash, the largest tributary of Bouse Wash, drains
Butler Valley and flows southwest through a narrow gap between the Bouse
Hills and the Granite Wash Mountains into the northeast corner of the
Ranegras Plain. Cunningham Wash joins Bouse Wash approximately 4 miles southeast of the town of Bouse. Bouse Wash, Cunningham Wash, and the numerous small tributary washes originating in the mountains flow only after a heavy rain. No perennial streams exist in the basin.
The drainage divide between the Ranegras Plain and McMullen
Valley is not in the Granite Wash Mountains at Granite Wash Pass, as expected, but rather in the basin fill approximately 1.5 miles northeast of the pass near the town of Harcuvar. Centennial Wash drains the remainder of McMullen Valley. Ross (1923) postulated that McMullen
Valley originally drained through Granite Wash Pass, but headward ero- sion by Centennial Wash captured the drainage.
28 29
Groundwater Hydrology
Occurrence of Groundwater
The basin fill of the Ranegras Plain is the major groundwater reservoir. Most groundwater occurs in the lower basin fill. The upper basin fill is generally above the water table in the northern half of the basin. The most productive wells are those perforated in the coarse- grained facies of the lower basin fill. The rocks of the surrounding mountains are dense and nonporous, and do not store or transmit signifi- cant quantities of groundwater. Locally fractured zones may transmit significant quantities of water.
Regional Groundwater Movement
Groundwater in the Ranegras Plain basin moves predominantly from the southeast to the northwest along the the basin axis. Water-level elevations for 1975 are shown on Figure 8. Outflow from the basin occurs a few miles northwest of Bouse, at the site of a subsurface groundwater barrier. Briggs (1969) reported a sharp water-level decline over 110 feet within a distance of 2 miles. Shallow bedrock at this location is confirmed by driller's logs.
Underflow from Butler Valley enters the northeast corner of the
Ranegras Plain, and travels southwest until it joins the regional flow toward Bouse. A groundwater barrier between the Bouse Hills and Granite
Water Mountains is indicated by a drop in water level from approximately
1,270 f.a.s.l. in western Butler Valley (Well B(7-15)9ddd) to 30
7.8N 4 c.
o 5 "P SCALE IN MILES Explanation ^960 Elevation of Water Table (1976) F.A.S.L. Source: Wilkins and Webb (1976)
Figure 8. Water-level elevation map. 31 approximately 917 f.a.s.l. in Well B(6-15)7bcd, 7 miles to the south- southwest in the Ranegras Plain basin.
Groundwater Recharge
Recharge to the Ranegras Plain basin occurs from four sources:
(1) infiltration from washes, (2) underflow from Butler Valley, (3) moun- tain front recharge, and (4) irrigation return flow.
The coarse, unconsolidated sand and gravel in Bouse Wash, Cun- ningham Wash, and their tributary washes are highly permeable, so large amounts of water may infiltrate when the washes flow.
Moderate rainfall produces little recharge through the soil in the Ranegras Plain, as shown by the common occurrence of caliche in the soil at depths from 0.5 to 20 feet. The majority of the water that infiltrates into soil is lost by evapotranspiration. The depth to the top of the caliche usually represents the deepest penetration of the infiltration front (Gile and Grossman, 1979). Old caliche may occur at depths greater than present surface infiltration penetration. Lake evaporation, an average estimate of potential evapotranspiration, varies between 78 and 80 inches per year (U.S. Weather Bureau, 1959).
The 1975 water-level contours indicate mountain-front recharge from the Plomosa Mountains, Bear Hills, and Granite Wash Mountains. Due to the large surface area and low permeability of the mountains sur- rounding the Ranegras Plain, large quantities of runoff are funneled into the numerous tributary washes leading into the basin. The sediment adjacent to the mountains is coarser than the basin interior; therefore, 32
infiltration rates are greater at the basin perimeter. Metzger (1951)
estimated 3,000 acre-feet per year (ac-ft/yr) of mountain front
recharge.
Underflow from Butler Valley cannot be quantified at this time
without additional depth-to-bedrock data. The 1975 water-level eleva-
tions measured in Butler Valley wells (Wilkins and Webb, 1976) varied
less than 5 feet; therefore, the hydraulic gradient within the Butler
Valley basin and the flux from Butler Valley into the Ranegras Plain
must be small.
The quantity of water recharged to storage from irrigation has
not been quantified, but is probably less than the other three types of
recharge. The average yearly pumpage for the period 1970 to 1975 was
only 18,000 ac-ft/yr, and all of this water was applied in areas where
the depth to water is between 100 and 300 feet (Wilkins and Webb, 1976).
Groundwater Discharge
Groundwater discharge from the Ranegras Plain basin occurs by pumping, underflow out of the basin near Bouse, and evapotranspiration.
Wilkins and Webb (1976) estimated groundwater pumpage in the
Ranegras Plain from 1950 to 1974 to total 332,000 acre-feet (ac-ft) and average 13,000 ac-ft/yr. The majority of the groundwater was used for agricultural irrigation. The average yearly pumpage from 1970 to 1975 was 18,000 ac-ft/yr. The quantity of water pumped in the Ranegras Plain is small compared to the more highly agriculturally developed basins in
Arizona, primarily due to the unsuitably high salt content of the water for some crops. 33
Metzger (1951) calculated the underflow at Bouse to be 7,500 ac-ft/yr based on an aquifer 100 feet thick and 2 miles wide, a hydrau- lic gradient of 70 feet per mile, and an average hydraulic conductivity of 500 gallons per day per square foot (gal/day/ft2).
Evapotranspiration losses from the aquifer are negligible. Only near Bouse is the water table sufficiently close to the land surface to support phreatophyte growth.
Metzger (1951) estimated a safe yield from the Ranegras Plain basin between 5,000 and 15,000 ac-ft/yr. Briggs (1969), assuming a specific yield from 0.15 to 0.20, calculated that 90,000 to 120,000 ac-ft of water was removed from storage from 1948 to 1967 based on water level declines. Recharge supplied the remainder of the 211,000 ac-ft pumped during this period (91,000 to 121,000 ac-ft). Therefore, recharge averaged from 4,500 to 6,000 ac-ft/yr.
Depth to Water and Water-table Elevations
In 1975, the water-table elevations ranged from 1,018 f.a.s.l. in the southern part of the basin [Well B(2-14)10cdc] to just under 900 f.a.s.l. in the vicinity of Bouse (Figure 4). The hydraulic gradient averaged 4.8 feet per mile (ft/mi) in the northern half of the basin and
1.7 ft/mi in the southern half.
Depth to water varied from approximately 50 feet in the vicinity of Bouse to over 300 feet in the southern third of the basin and on the eastern margin of the basin within 3 miles of the Granite Wash Mountains
(Wilkins and Webb, 1975). Depth to water generally increases to the south and towards the basin perimeter. 34
Water-level decline in the majority of the basin ranged from 10 to 20 feet from 1948 to 1975 with the exception of the western half of
T. 5 N., R. 15 W., which experienced a decline of 20 to 25 feet.
Well Yields
Most high capacity wells in the Ranegras Plain are screened in the coarse-grained facies of the lower basin fill. These wells are usually at the basin perimeter, where the coarse-grained facies occurs at depths less that 150 feet. High capacity wells in the basin center are sufficiently deep to go through the fine-grained facies and pene- trate the underlying coarse-grained facies.
Irrigation wells in the western half of T. 4 N., R. 14 W., and the northeastern quarter of T. 4 N., R. 15 W., are just east of the boundary between the fine- and coarse-grained facies of the lower basin fill (Figure 4). These wells have casing diameters of 16 or 20 inches and depths from 905 feet to 1,002 feet below land surface; well yield varies from 3,000 to 4,000 gallons per minute (gpm).
Wells perforated in the fine-grained facies are generally poor producers. Well B(4-14)30cca, which is drilled into the fine-grained facies, is an 8-inch-diameter well drilled to a depth of 250 feet. The well yield is only 6 gpm. Well B(4-15)8aacl, located in the basin cen- ter, is an 8-inch well, with a depth of 420 feet and a discharge of only
27 gpm.
Wells drilled deep enough to go entirely through the fine- grained facies (i.e., deeper than 1,000 feet), may attain a yield greater than 2,000 gpm. For example, Wells B(4-15)18BBB and 35
B(4-15)18bbc [Figures 4 and 6] are 20-inch-diameter wells drilled within half a mile of each other. The former has a depth of 670 feet and a yield of 670 gpm, and the latter has a depth of 1,242 feet and yields
2,000 gpm.
Production wells near the town of Utting in the southeastern quarter of T. 6 N., R. 16 W. are generally 20-inch diameter and 1,000 to
1,300 feet deep, and yield 2,300 to 2,600 gpm.
Specific Capacity and Transmissivity
Specific capacity ranges from 1.9 to 23.9 gallons per minute per foot (gpm/ft). Wells screened entirely in the fine-grained facies have the lowest specific capacity (SC), for example, Well B(2-14)10cdc
(SC = 2.94 gpm/ft) and Well B(5-15)32ddd (SC = 1.9 gpm/ft). The highest specific capacities in the basin were obtained from Well B(6-16)26aad
(SC = 20.3 gpm/ft) and B(6-16)33aaa (SC = 23.9 gpm/ft). Both wells are in the vicinity of Utting. These wells are screened in the coarse- grained facies of the lower basin fill and intersect over 500 feet of sand and gravel.
The only aquifer test data available were for Well B(3-14)12ccc, located just west of the Black Rock Hills. The coefficient of transmis- sivity is 160 gallons per day per foot (gpd/ft). This well is perfo- rated in the fine-grained facies; and, therefore, its transmissivity is not indicative of the high capacity wells. CHAPTER 4
GEOCHEMISTRY OF STRONTIUM
This chapter presents a brief literature review of strontium geochemistry. Although the main emphasis is on strontium hydrogeo- chemistry, a brief discussion of the occurrence of strontium in igneous, metamorphic, and sedimentary rocks is included.
Chemical Behavior of Strontium
Strontium is an alkaline-earth metal with an atomic number of
38. The electron distribution in the strontium atom (ls 22s22p63s23p63d10_
4s 24p 6 5s 2 ) results in the universal divalency in its compounds (Skougs- tad and Horr, 1963). Four stable isotopes of strontium exist with mass numbers of 84, 86, 87, and 88. The natural distribution of these iso- topes produces an average atomic weight for strontium of 87.63 grams per mole (Faure, 1977). No radioactive isotopes of strontium exist in nature, but as many as 10 artificially produced radioisotopes have been identified. Two of these isotopes, strontium-89 and strontium-90, are among the most hazardous components of radioactive waste, because stron- tium is readily assimilated into human bones, where damage to bone mar- row may occur. Therefore, the U.S. Environmental Protection Agency has specified a maximum safe level for strontium-90 in drinking water of 8
36 37
picocuries per liter [pCi/1] (U.S. Environmental Protection Agency,
Office of Water Supply, 1976).
The most abundant alkaline-earth elements in the earth's crust
and the hydrosphere are calcium and magnesium. Next in order of general
abundance are strontium and barium, frequently of the same order of
magnitude. The ionic radius and ionic potential of strontium is inter-
mediate between calcium and barium and similar in magnitude to that of
potassium, thereby allowing strontium to substitute in calcium and
barium minerals, and to a lesser extent in potassium minerals (Skougstad
and Horr, 1963).
Strontium Minerals
Strontium forms chemical compounds analogous to those of calcium
and barium. The carbonates, sulfates, chromates, and phosphates are
sparingly soluble in water (King, 1959). The two most common strontium
minerals are strontianite (SrCO 3 ) and celestite (SrSO 4 ). Strontium
chromate and phosphate are only rarely found in nature.
Strontianite
"Strontianite is a low-temperature hydrothermal mineral asso-
ciated with barite, celestite, and calcite in veins in limestone or marl, and less frequently in igneous rocks and as a gangue mineral in sulfide veins" (Hurlbut, Jr. and Klein, 1977). In the United States strontianite occurs in geodes and veins with calcite at Schoharie, New
York, in the Strontium Hills north of Barstow, California (Durell, 38
1953), near La Cormer, Washington (Landes, 1929), and associated with
fluorite deposits in Southern Illinois (Grawe and Nackowski, 1949).
Celestite
Celestite occurs primarily as finely disseminated crystals in
limestone or sandstone or in cavities of these rocks. It is associated with calcite, dolomite, gypsum, halite, sulfur, and fluorite, or occurs
as a gangue mineral in lead veins (Hurlbut, Jr. and Klein, 1977).
Celestite occurs in the United States at Clay Center, Ohio; Mineral
County, West Virginia; Lampasas, Texas; and Inyo County, California.
Factors Controlling Formation of Strontium Minerals
Strontium minerals occur in volcanic, alkali, and hydrothermal deposits, especially in arid regions like California (Durrell, 1953).
Vinogradov and Borovik-Romanova (1945) postulated that strontium min- erals are an indicator of arid climate at time of formation due to the tendency for evaporite deposits in Russia to contain strontium minerals.
Strontium minerals are associated with evaporite deposits in New York,
Michigan, California, and Louisiana (Odum, 1957b).
At low temperatures, strontium minerals form during the diagen- esis of limestones, dolomite, shales, and evaporites. Many examples exist of secondary deposits of celestite and strontianite, such as celestite encrusting ammonite casts (Jayoraman, 1940) and replaced
Paleozoic limestones in New York and Ohio (Stout, 1941). Low tempera- ture replacement processes are responsible for the formation of celes- tite in the cap rocks of salt domes in Texas (Wolf, 1926; Brown, 1931), 39
Russia (Pitkovska, 1939), and Sicily (Noll, 1934). During the evapora-
tion of saline waters, celestite can deposit between limestone-dolomite beds and gypsum-anhydrite beds. The deposition of limestone-dolomite
increases the Sr/Ca ratio, so that the SrSO4 solubility product is exceeded before the CaSO4 solubility product (Vinogradov and Borovik-
Romanova, 1945).
Strontium As a Minor Constituent of Minerals
Most strontium occurs as a minor constituent of minerals and rocks rather than in the form of the two most common strontium minerals, strontianite and celestite. Strontium can occur as a trace element by three mechanisms: solid solution crystal substitution, crystal occlu- sions, and adsorption. The following two sections discuss the occur- rence of strontium as a minor constituent in igneous and sedimentary rocks.
Igneous Rocks
Historically, the occlusion of strontium into other minerals was interpreted as substitution for a major ionic constituent of similar ionic radius (Odum, 1957b). Noll (1934) reported the positive correla- tion of strontium with calcium and potassium. Holmes and Harwood (1932) positively correlated strontium with potassium. These relationships appeared to be explained by the diadochic replacement principle (Gold- schmidt, 1937; Rankama and Sahama, 1950; Odum, 1957b), which states that certain minor elements tend to substitute for major elements that have similar radius and bond type. Strontium follows this rule, and is 40 usually present primarily in the calcium-rich minerals, and secondarily in high-temperature potassium minerals (Turekian and Kulp, 1956).
Analysis of 244 basaltic rocks from locations through out the world demonstrated no marked universal covariance of strontium and cal- cium (Turekian and Kulp, 1956). They attributed this observation to regional differences in strontium content of the source magma and the local effects of fractional crystallization and magmatic differentia- tion. Turekian and Kulp (1956) estimated a crustal abundance of stron- tium in basaltic rocks of 465 parts per million (ppm). Differentiated basaltic bodies such as the Stillwater complex (Turekian and Kulp, 1956) and the Skaergaard intrusion (Wagner and Mitchell, 1951) show an increase of strontium content as the calcium content decreases. In the
Basin-Range Province, widespread Tertiary basaltic and andesitic flows exhibit a high average strontium concentration of 943 ppm (Turekian and
Kulp, 1956).
Holmes and Harwood (1932) and Noll (1934) discussed the correla- tion of strontium occlusion with rapid magmatic cooling. Volcanic and aphanitic rocks have a higher strontium content than slowly-cooled, coarse-grained rocks (Turekian and Kulp, 1956). The slow crystalliza- tion permits strontium excluded from the crystal lattice to be deposited in differentiated magma, pegmatites, or alkali rocks.
Turekian and Kulp (1956) showed that strontium content in granitic rocks increases with an increase in calcium. The average strontium content of granite was reported to range from 160 ppm (Africa) 41 to 337 ppm (Western U.S. - Mesozoic), and to average 328 ppm in the
Rocky Mountains.
Sedimentary Rocks
The average concentration of strontium was reported to be 700 ppm in shale (Shaw, 1954), 20 ppm for shales and phyllites (Hevesy and
WUrstlin, 1934), and 300 ppm for shales (Turekian and Kulp, 1956). Odum
(1957b) observed that the strontium content of pelitic rocks is indepen- dent of the calcium content. Strontium occurs in both the carbonate fraction and adsorbed to the clay particles of pelitic rocks and sedi- ments (Turekian and Kulp, 1956). The occurrence of strontium in the sediments of open and closed drainage lakes is reviewed in Chapter 7 and compared to data from the Ranegras Plain basin.
Strontium averages 500 ppm in limestones and is present within the structure of the calcium carbonate minerals (Blatt, Middleton, and
Murray, 1980). The crystal structure of aragonite accommodates the relatively large atomic radius of strontium more easily than calcite.
Thus, calcitic limestone may contain up to 1,000 ppm strontium, whereas aragonitic limestone may contain greater than 10,000 ppm strontium. The ionic spacings of the orthorhombic aragonite crystal system can more easily occlude strontium than the polymorphous mineral calcite, which has the same chemical composition, but a rhombohedral crystal system
(Odum, 1957b).
Odum (1957b) reported strontium concentrations in a series of non-biological crystals of calcite and aragonite ranging from 310 to
8,100 ppm for calcite and 610 to 15,400 ppm for aragonite. Variations 42 of strontium concentrations in limestone are due to the Sr/Ca ratio in the liquid phase from which the solid is derived, the polymorph into which the strontium is precipitated (calcite or aragonite), temperature, salinity, and the ratio of deposition (Turekian and Kulp, 1956; Odum,
1957b; Swan, 1956; Lowenstam, 1954). The relationship is further com- plicated by the diagenesis of aragonite to calcite and the subsequent removal of strontium by groundwater.
Strontium in Isomorphous Series
Although the substitution of strontium for calcium as a minor component in minerals is common, the substitution of strontium in large enough amounts to form a solid-solution series from one non-strontium mineral to an isomorphous strontium mineral occurs in only a few cases
(Odum, 1957b). Isomorphic substitution series occur between strontium and barium sulfates (Grahmann, 1920) and strontium and calcium silicates
(Eskola, 1922; Rankama and Sahama, 1950; Toropov and Konovalov, 1943).
Occurrence of Strontium Mineral Deposits in California and Arizona
A number of significant celestite and strontianite deposits occur within 200 miles of the Ranegras Plain in the Mohave Desert area of southern California and in southwestern Arizona (Durrell, 1953; Phalen,
1912; Moore, 1935; and Knopf, 1918). These strontium deposits are found at the following locations: (1) near Ocotillo, California, (2) the
Bristol Dry Lake deposit near Amboy, California, (3) at the southern end of Death Valley, (4) the Soloman and Ross deposits near Barstow, Califor- nia, (5) near Ludlow California, and (6) west of Gila Bend, California. 43
These deposits occur in association with with playa evaporite deposits
and Tertiary volcanic tuffs and flows. Durrell (1953) proposed three
potential sources for the strontium in these deposits: (1) the weather-
ing of rocks in the drainage basin followed by concentration in the
playa waters by evaporation and subsequent strontium mineral precipita-
tion, (2) the presence of strontium as a significant trace constituent
of pyroclastic rocks or lava flows deposited directly into the playa and
subsequent release of strontium in soluble form by the alteration of
rocks, and (3) the release of hydrothermal solutions or mineralized
spring waters of juvenile origin from igneous sources to the surface of
the drainage basin or directly to the playa.
Celestite deposits occur as a 2- to 8-foot thick cap overlying
bedded gypsum in Tertiary sedimentary rocks near Ocotillo, San Diego
County, California (Durrell, 1953).
The Bristol Dry Lake deposit near Amboy, San Bernardino County,
California consists of concretions of celestite in sandy gypsiferous
clay and in thin-bedded sands at the margin of the playa. Strontium is
present in the sediment below the concretions and in the waters of the
playa, suggesting that concretions are forming at present. Durrell
(1953) attributed the strontium source to Tertiary basalts and andesites
adjoining the dry lake. Adjoining the lake in the vicinity of the
strontium deposit and partially buried beneath the surface layers of
clay is a large body of olivine basalt.
At the southern end of Death Valley, celestite is deposited as beds and concretions in gypsum, gypsiferous clay, clay, and sandstone. 44
The largest bed is 13 feet thick. Moore (1935) proposed that the
celestite is sedimentary in origin. Durrell (1953) concluded that the
celestite was formed by precipitation from connate waters within the
sediments, based on the presence of large celestite concretions which
truncate the bedding of the enclosing sediments and which are not inter-
nally bedded.
The Soloman and Ross strontianite deposits are half a mile apart
in the east end of the Mud Hills, northeast of Barstow, California. The
Soloman strontianite occurs as bedlike and crosscutting bodies that
replaced volcanic tuffs, tuffaceous bentonite clay beds, and tuffaceous
marls (Durrell, 1953; Knopf, 1918). Durrell supports the hydrothermal
origin of the strontianite, because the occurrence of the mineral is
controlled by both sedimentary structures and faults, and botryoidal masses of strontianite containing chalcedony are present. The Ross
strontianite deposit consists of alternating thin-bedded green clay and
strontianite beds. Knopf (1918) concluded that the strontianite had
replaced limestone; however, Durrell (1935) concluded that the clay was
the original rock and strontium in solution in the lake water probably originated: (1) from igneous activity and was carried into the lake with
the volcanic tuffs that are so abundant in the section, (2) by volcanic emanation, or (3) by juvenile spring waters.
Celestite beds and concretions near Ludlow, San Bernardino
County, California, occur in lacustrine thin-bedded tuffs and clays that are the highest exposed rocks of the Tertiary system (Durrell, 1953).
The celestite appears to have precipitated after deposition of the tuff 45
and clay from waters contained in the sediments. The presence of some
intensely silicified lake sediments supports the theory of the hydro-
thermal origin strontium.
Celestite occurs with gypsum, sandstone, and conglomerate at a
location 15 miles west of Gila Bend (Phalen, 1912). The series is
associated with igneous flows and intrusions. The celestite occurs as a bed or beds overlain and underlain by sandstone beds and igneous flows.
Strontium Hydrogeochemistry
This section summarizes the aqueous geochemistry of strontium in natural waters. Included are brief summaries of the literature on
strontium concentrations in natural waters, geologic conditions accom- panying high strontium concentrations in groundwater, studies using
strontium as a hydrogeochemical tracer, and strontium isotope hydrogeo- chemistry.
Strontium Concentrations in Natural Waters
In a survey of 75 major rivers and 175 groundwater samples in the United States, Skougstad and Horr (1963) reported that the strontium concentrations in surface water ranged from 0.007 to 13.7 milligrams per liter (mg/1). Sixty percent of the groundwater samples contained less than 0.2 mg/1, although some potable groundwater samples contained as much as 50 mg/l. Brines contained up to 2,960 mg/l. The greatest strontium concentrations in surface water were found in the high salin- ity streams of the southwestern United States. 46
Alexander, Nusbaum, and MacDonald (1954) in a study of the
occurrence of strontium in the water supplies of 50 major cities in the
United States reported a range of strontium content from 0.0058 mg/1 to
1.9 mg/1 in untreated surface water or groundwater used for municipal
supply. Only two sources contained more than 1 mg/l.
Nichols and McNall (1957) completed a comprehensive survey of
the strontium occurrence in municipal water supplies in Wisconsin.
Water in the eastern part of the state usually contained more than 1.0
mg/1 strontium, and several wells in this area contained strontium con-
centrations exceeding 30 mg/l.
A survey of the strontium content of the drinking water in
Chicago, Denver, Oak Ridge, Cincinnati, New York, Atlanta, and Char-
lottsville (Blanchard, Leddicotte, and Moeller, 1958) reported strontium
concentrations from 0.08 to 1.23 mg/l.
Strontium concentrations ranged from 0.02 to 22 mg/1 in ground-
waters and from 0.02 to 1.25 mg/1 in surface waters from the Paris
Basin, France (Carré and Pinta, 1979). The strontium concentration in
rainfall varied from 0.02 to 0.05 mg/l.
Durum and Haffty (1963) reported that of the 15 or more minor
elements in the world's principal river waters, only aluminum, iron, manganese, barium, and strontium exceed 100 micrograms per liter (ug/l).
They reported strontium concentrations in the water of large rivers of
North America ranging from 0.0063 to 802 ug/1 and averaging 60 ug/l. 47
Geologic Condition Accompanying High Strontium Concentrations in Groundwater
The predominant sources of strontium in natural waters are the trace amounts of strontium found in nearly all sedimentary, igneous, and metamorphic rocks. High concentrations of strontium in groundwater occur in three types of hydrogeologic environments: (1) areas where isolated celestite and strontianite lenses occur in glacial till and limestone, (2) geologically recent limestone aquifers where the diagen- esis of aragonite to calcite occurs, and (3) aquifers in contact with evaporites and brines. These environments are discussed in the follow- ing three subsections.
Celestite and Strontianite Occurrences in Glacial Till and
Limestone Aquifers. Celestite frequently occurs as a disseminated secondary mineral in limestone and dolomite. Isolated lenses of celes- tite and strontianite may also occur as secondary mineralization in glacial till. The Sr/Ca molar ratio (Sr atoms per 1,000 Ca atoms) of most groundwaters usually does not differ greatly from that of the par- ent rock and is less than 10 for the majority of groundwaters; however, groundwater in contact with celestite or strontianite may have Sr/Ca ratios as high as 150 (Skougstad and Horr, 1963).
Feulner and Hubble (1960) reported on the occurrence of stron- tium in surface water and groundwater in Champaign County, Ohio. They found strontium concentrations up to 30 mg/1 in well waters from celestite-rich limestones and glacial deposits of late Silurian age.
The Sr/Ca ratios of the eight samples ranged from 89 to 132. 48
Foley, Bleuer, and Leininger (1972) observed strontium concen- trations up to 15 mg/1 in groundwater from glacial till and Devonian carbonate aquifers in Allen County, Indiana. They attributed these elevated concentrations to the selective dissolution of soluble evapor- ites or their residues in the carbonate bedrock and the subsequent accumulation of residual celestite. The Sr/Ca molar ratios of the groundwater samples were as high as 154.
Stueber, Baldwin, and Pushkar (1973) in a study of elevated strontium concentrations (10 to 45 mg/1) in groundwater from the Scioto
River Basin, Ohio, analyzed 87 Sr/ 86 Sr ratios in the Paleozoic carbonate aquifer, glacial till, and groundwater samples. They concluded that the high strontium was due primarily to leaching of celestite in the glacial till and carbonate bedrock.
Limestone Aquifers Undergoing the Diagenesis of Aragonite to
Calcite. As groundwater passes through a limestone aquifer, metastable carbonate (aragonite or high-magnesium calcite) will dissolve incongru- ently with the simultaneous precipitation of purer carbonates (low- magnesium calcite) which contain lower concentrations of strontium
(Kinsman, 1969; Edmunds, 1980). This process releases strontium into the groundwater. Most aragonite contains 8,000 to 10,000 ppm strontium
(Morrow and Mayers, 1978). Generally, high-magnesium calcite ranges from 1,000 to 3,000 ppm strontium. The strontium concentration in most low-magnesium calcite ranges from 1000 to 2,000 ppm. Ancient limestones contain far less strontium than recently deposited limestones (Kinsman, 49
1969). Many ancient limestones contain only tens or hundreds of ppm strontium.
The maximum strontium concentration in groundwater due to arago- nite diagenesis was reported to be 13.3 mg/1 in Barbados (Harris and
Matthews, 1968) and 16.6 mg/1 in Barbuda (Wigley, 1973). Edmunds (1980) postulated that strontium concentrations in groundwater ranging up to 29 mg/1 in the Sirt Basin, Libya were due to the diagenesis of aragonite.
The aqueous strontium concentrations in aquifers composed of high- magnesium calcite and low-magnesium calcite will be lower than these levels and dependent on the strontium concentration in the source rock.
Models of limestone diagenesis have been developed as a tool to determine the mechanisms and rate of limestone diagenesis (Kinsman,
1969; Morrow and Mayers, 1978). Kinsman (1969) demonstrated that the strontium concentrations of diagenetically altered limestones are of potential value in indicating the mechanism of diagenesis. He presented conceptual models of closed-system and open-system recrystallization of carbonate sediments in the presence of aqueous solutions. Morrow and
Mayers (1978) simulated limestone diagenesis with a computer model based on strontium depletion in meteoric ground water. The model predicted that 3000 to 6000 pore volumes of meteoric groundwater are required to transform aragonitic limestones in Barbados and Barbuda to low-magnesium calcite with average strontium contents of 1700 ppm and 500 ppm stron- tium, respectively. The model further predicted that during the recrys- tallization of low-magnesium calcite, tens of thousands to hundreds of thousands of pore volumes of meteoric water must pass through limestones 50
to reduce their strontium contents to between 100 and 200 ppm. The abnormally high concentration of strontium retained in hydrocarbon- bearing limestones were postulated to be due to the inhibition of the solution-reprecipitation process by the hydrocarbons. Nadler et al.
(1980) and Schroeder (1969) studied the kinetics affecting the dissolu- tion of strontium and other trace elements from carbonate rocks.
Aquifers in Contact with Evaporites and Brines. Elevated strontium concentrations in groundwater are commonly due to the dissolu- tion of evaporites in which strontium is a trace constituent of gypsum or anhydrite. Celestite is a common minor accessory mineral in gypsum and anhydrite deposits, and occurs in greater quantities as secondary masses replacing sulfates (Stewart, 1963). Where groundwater contacts these deposits, elevated strontium concentrations and Sr/Ca ratios will occur.
Skougstad and Horr (1963) reported the chemical analyses of subsurface brines from California, Michigan, North Dakota, and West
Virginia with strontium concentrations from 11 mg/1 to 2,960 mg/l. The
Sr/Ca molar ratios in these samples ranged from 4.4 to 28.6.
Melchior, Rogers, and Langmuir (1986) investigated deep brines in the Palo Duro Basin, Texas to assess the fate of radionuclides that might be released to those brines from a repository in overlying salt beds. They evaluated chemical equilibria of the brines with a geochem- ical model modified to accommodate the brine temperatures (32-40°C) and pressures (67-130 bars). The brines, which are located within limestone and dolomite, were saturated with respect to gypsum, anhydrite, and 51 celestite. Three of the five brines were saturated with respect to barite.
Additional examples of hydrogeologic investigations of brines and groundwaters in contact with evaporites are included later in this chapter in the section "Hydrogeologic studies using strontium isotope geochemistry".
Previous Studies Using Strontium as a Hydrogeochemical Tracer
A number of researchers employed strontium as a naturally occur- ring tracer in groundwater investigations. Edmunds (1971) used stron- tium and fluoride to distinguish groundwater originating from base metal mineralized areas. Edmunds, Owens, and Tate (1976) used potassium and strontium to quantify induced recharge from rivers into aquifers.
Strontium was used to assist the understanding of the diagenesis of groundwaters in two carbonate aquifers in England, the Lincolnshire
Limestone (Edmunds, 1973) and the Cretaceous Chalk (Edmunds, 1976). In the study of the Sirt Basin, Libya, Edmunds (1980) used strontium con- centrations along with other geochemical and hydrogeologic information to distinguish marine-derived groundwaters from nonmarine-derived waters, to trace the extent of leakage from one aquifer to another, and to define hydrogeochemical facies and evolution along flow paths within the aquifers.
Hydrogeologic Studies Using Strontium Isotope Geochemistry
A number of researchers used the 87 Sr/ 86 Sr ratio of groundwater to determine its provenance. Groundwater attains the same isotopic 52
ratio as the rocks with which it has contact. 87 Sr is the daughter product of the radioactive decay of 87 Rb, and its abundance •has, there-
fore, increased throughout geologic time. For this reason, the stron-
tium isotope ratio of a rock or mineral depends on the age and Rb/Sr ratio of that rock or mineral (Faure, 1977). In general, Rb-rich rocks such as shales have relatively high present 87 Sr/ 86 Sr ratios, and
Rb-poor rocks such as carbonates have low 87 Sr/86 Sr ratios.
Numerous workers studied the systematic variations in the 87 Sr/ 86 Sr ratio of sea water through Phanerozoic time. Assuming the isotopic ratio of the ocean is homogeneous at any given time, the ratio measured in marine carbonates, evaporites, and phosphates determines their age. Burke et al. (1982) presented a detailed curve of seawater
87 Sr/ 86 Sr versus geologic time through the Phanerozoic by the isotopic analysis of samples of samples of known age. Recently, Hess, Bender, and Schilling (1986) improved the resolution of the last 100 million years by the determination of the 87 Sr/ 86 5r in fossil foraminifera.
Stueber, Pushkar, and Baldwin (1972) analyzed total strontium concentrations and 87 Sr/ 86 Sr ratios in 19 Ohio stream waters and 4 groundwaters in order to determine the usefulness of the 87 Sr/ 86 Sr ratio as an indicator of water provenance. The measured ratios ranged from
0.7078 to 0.7130, with the higher ratios occurring in areas of predom- inantly clastic sediments, and the lower ratios occurring in areas of limestone bedrock or glacial till containing soluble carbonates.
Analysis of strontium isotope ratios and Sr/Ca ratios in additional groundwater samples (Stueber, Baldwin, and Pushkar, 1973; Stueber et 53 al., 1975) indicated that the high strontium concentrations in ground- water were due to leaching of celestite from carbonate bedrock and glacial till. Stueber et al. (1975) could not determine a unique source of the strontium in the groundwater, because tnethe Sr/ 86 Sr ratio of the celestite was very similar to that of the carbonate bedrock.
A sampling of the 39 largest Canadian rivers showed that the 87 weighted average Sr/ 86 Sr ratio of the dissolved strontium is 0.7111, similar to previous measurements on large rivers as the Amazon and
Mississippi (Wadleigh, Veizer and Brooks, 1985). Evaluation of geological information suggests that strontium from silicate sources is of considerable importance for all but the largest Canadian rivers.
A number of investigations on the 87 Sr/ 86 Sr ratio of oil field brines were completed to determine the sources of dissolved strontium in these brines and their migration history (Chaudhuri, 1978; Sunwall and
Pushkar, 1979; Starinsky et al., 1983). These investigations show a wide range of 87 Sr/ 86 Sr ratios in oil-field brines (0.7075-0.7341).
Stueber and Pushkar (1983) analyzed the 87 Sr/ 86 Sr ratio in 40 oil field brines from the Upper Jurassic Smackover Formation in southern
Arkansas. Since the brines are more radiogenic than Jurassic seawater, they concluded that a significant proportion of the strontium dissolved in these brines was acquired from a source material that did not form entirely by precipitation of Jurassic seawater. The strontium isotope analyses of rock units associated with the brines (Stueber, Pushkar, and
Hetherington, 1984) suggest that the radiogenic strontium was released from detrital minerals from a shale unit, and mixed in variable 54 proportions with the strontium-rich marine waters that had the isotopic composition of Late Jurassic sea water. This accounted for the variable
87 Sr/ 86 Sr ratios observed in the brines within the 5000 km 2 study area.
Pushkar, Stueber, and Hetherington (1983) concluded that the strontium isotope ratio of anhydrite, calcite, and celestite from the Vacherie salt dome in the North Louisiana salt basin were characteristic of mar- ine strontium during the Jurassic (0.7068), supporting the commonly- accepted theory that the salt dome originated from the Jurassic Louann salt.
Posey, Price, and Hurst (1985) studied the 87 Sr/ 86 Sr ratio of anhydrite cap rocks from Gulf coast salt domes. The anhydrites showed remarkable isotopic variation within domes along the margins of the mid-
Jurassic Gulf Coast (0.7070-0.7100), indicating mixing between seawater and radiogenic, meteoric, or continental hydrothermal fluids.
Posey, Wessel, Fullagar, and Price (1986) studied the 87 Sr/ 86 Sr ratio of salt dome cap rock and calcites of the Hockley Dome, Texas, to test the theory that cap rock sulfide minerals formed from brines. The authors concluded that a low-strontium, high 87 Sr/ 86 Sr material mixed with a high-Sr, low ratio material (probably the Louann evaporite deposits) to form the cap rock and calcites.
The strontium isotopic composition of deep brines from the
Precambrian shield of Canada were investigated by McNutt, Frape, and
Fritz (1984). Each geographic location had a limited range of 87 Sr/ 86 Sr ratios distinct from the others, apparently due to extensive water-rock interaction on a local scale. Strontium showed a strong positive 55 correlation with calcium and bromine, indicating a common source for the three elements.
An analysis of the "Sr/"S r ratios from hot and carbonated springs in the Peninsular Ranges of southern California and Baja, Cali- fornia indicated that the strontium ratios of these deeply circulated spring waters could be divided into two groups, a western terrane with ratios of 0.7067-0.7056, and an eastern terrane with water of 0.7067-
0.7077 (Gastil et al., 1984). The strontium ratios appear to reflect the regional variation in the strontium ratios of granitic rocks rather than that of the metasedimentary rocks.
The strontium concentrations and 87 Sr/ 86 Sr ratios of ground- waters from the Great Artesian Basin in central and northeastern
Australia vary significantly (Collerson, Ullman and Torgersen 1986).
Both the strontium concentrations and the isotopic ratios correlated with distance from the recharge area and age of the waters. Samples from the recharge area are enriched in calcium relative to the basin water and have 87 Sr/86 Sr ratios ranging from 0.70446 to 0.70534. Waters from the basin center are significantly more radiogenic and have
87 Sr/ 86 Sr ratios as high as 0.71176. CHAPTER 5
HYDROGEOCHEMISTRY OF THE RANEGRAS PLAIN BASIN
This chapter discusses the major ion hydrogeochemistry of groundwater in the Ranegras Plain basin. The concentrations and distri- bution of major ions are described and correlated with geology and hydrology. Evaluation of chemical analyses of groundwater provides evidence for mineral saturation, groundwater recharge, the weathering of silicate minerals, the dissolution of evaporites, and cation exchange within the basin aquifer.
Summary
The Ranegras Plain basin contains groundwater of high total dissolved solids characteristic of closed drainage basins. Total dis- solved solids generally range from 500 to 2000 mg/1; a sample from one well exceeds 4000 mg/l. The highest mineral content in groundwater occurs in the north central part of the basin. The chemical type of the groundwater is predominantly sodium chloride-sulfate.
Groundwater samples from wells located in recharge areas demon- strate comparably low pH values, high bicarbonate concentrations, and lower percent sodium values than the majority of the wells in the basin.
Basin-wide averages of mineral saturation indices demonstrate that the groundwater is saturated with respect to calcite, illite,
56 57 chalcedony, barite, and fluorite. Groundwater from a few individual wells are saturated with respect to aragonite, dolomite, and gypsum.
The hydrogeochemistry of the basin is dominated by the dissolu- tion of evaporites, primarily gypsum, as shown by three lines of evi- dence: (1) elevated concentrations of sodium, calcium, chloride, and sulfate in groundwater samples from many of the deep interior wells,
(2) the presence of gypsum in drill cuttings, and (3) comparison of the water chemistry of samples from nearby wells.
The weathering of silicate minerals is a significant contribut-
ing factor to the hydrogeochemistry of the basin. Silicate mineral hydrolysis is shown by mineral saturation indices, mineral stability diagrams, the high dissolved silica concentrations in groundwater, and elevated groundwater pH values. Hydrogen ions are consumed by silicate hydrolysis as recharged groundwater reacts with the aquifer sediments.
The rise in pH results in the precipitation of calcite within the aqui- fer matrix.
Cation exchange of sodium for calcium significantly reduces the calcium released from the dissolution of gypsum and silicate mineral weathering. Comparison of the water chemistry of nearby groundwater samples provides evidence for cation exchange.
Source and Analysis of Groundwater Quality Data
Fred N. Robertson of the U.S. Geological Survey, Water Resour- ces Division, Tucson, Arizona provided the chemical analyses of ground- water samples from the Ranegras Plain basin used for this investigation.
Robertson and his assistants sampled the groundwater from 42 groundwater 58 wells in the Ranegras Plain during the summer of 1980 and measured the pH, temperature, and alkalinity of each sample in the field. The U.S.
Geological Survey Water Laboratory analyzed the samples for major ions, trace elements, and nutrients. The water quality analyses are listed in
Table 1. For ease of reference within this thesis, each well was assigned a numeric well number; the state well numbers based on town- ship, range, and section, as used by the U. S. Geological Survey, are also provided in Table 1. Well construction details are summarized in
Table 2. Well locations are shown on Figure 9.
Fred Robertson and this author processed all groundwater analy- ses with the WATEQF geochemical speciation program (Plummer, Jones and
Truesdale, 1976). The WATEQF program uses the laboratory groundwater analysis, field pH, alkalinity, temperature, and, if available, dissolv- ed oxygen or Eh value as input data. WATEQF computes the concentration of each possible aqueous species (based on the input data) by iterative calculations of the activity of each species, and the ionic strength of the solution, and geochemical equilibria. After convergence of mass balance, the activity coefficient and the concentration of each aqueous species is printed as parts per million, molality, and activity. For each mineral that can be calculated, based on input data and available thermodynamic data within the program, WATEQF calculates the following quantities: (1) log io (AP), the log of the ion activity product,
(2) logio (KT), the log of the equilibrium constant at the sample temper- ature, and (3) log io (AP/KT), the mineral saturation index. When the groundwater sample is saturated with respect to a mineral, the 59 Table 1. Chemical analyses of groundwater samples.
2+ 2+ 2+ 2- 2- Well State Sr TDS pH Ca Mg Na K Cl SO HCO CO F - Si [Sr]/[Ca] Sodium (a) Number Well (cale) 4 3 3 molar ratio Percent Number (mg/1) (mg/1) (mg/1) (mg/1) (mg/1) (mg/1) (mg/1) (mg/1) (mg/1) (mg/1) (mg/1) (mg/1) (x 1000) (meq/1)
1 B(2-13)19ccc 0.090 580 8.4 9.0 2.3 180 6.6 87 180 126 3 8.2 36 4.6 90.7 1.88 2 B(2-14)10cdc 0.063 449 8.4 7.4 1.3 150 7.1 81 84 152 2 9.2 36 3.9 90.8 2.72 3 B(2-14)28ccc 1.0 703 7.9 47 2.9 130 4.3 120 130 134 0 0.5 31 9.7 94.2 -0.22 4 B(3-14)09ddd 0.075 705 8.1 7.2 4.4 240 2.9 150 120 232 0 9.7 4.8 92.9 3.94 5 B(3-14)13add 1.4 740 7.2 94 9.5 140 4.3 180 180 180 0 2.6 29 6.8 87.2 -2.28 6 B(3-15)02dac 618 8.2 7.4 0.4 220 1.1 180 120 66 0 12 20 95.7 2.04 7 B(3-15)02dab 0.20 699 8.3 12 1.1 210 2.5 170 160 84 0 10 21 7.6 98.3 1.11 8 B(3-15)23bdb2 0.076 451 8.3 11 6.3 140 3.9 91 110 118 0 4.4 3.2 90.8 1.56 9 B(4-14)04aac 0.26 275 8.1 4.2 0.5 91 2.7 32 45 148 0 0.9 28.3 92.5 2.21 10 B(4-14)18cdd 0.12 632 8.3 7.9 0.7 220 2.4 150 130 133 0 11 7.0 94.9 2.72 11 B(4-14)29cdd 0.060 588 8.4 5.1 0.8 210 2.1 140 110 136 3 9.2 5.4 96.1 2.98 12 B(4-15)08acc2 0.40 1150 7.6 37 1.4 350 2.2 290 270 182 0 6.7 4 • 9 98.9 1.53 13 B(4-15)09ada 1660 7.7 130 5.0 400 4.7 330 680 42 0 4.1 21 97.0 -5.77 14 B(4-15)09bad 1150 7.8 84 1.5 300 4.4 290 360 42 0 4.4 98.2 -2.46 15 B(4-15)18bbb 4.1 1530 7.7 260 3.1 200 4.4 138 780 88 0 5.3 7.2 95.9 -11.21 16 B(4-15)18bbc 601 7.7 27 4.9 170 3.7 120 170 58 0 3.6 93.7 0.74 17 B(4-15)28bbd 0.22 793 8.2 23 3.2 240 3.3 240 160 66 0 0.5 32 4.4 96.8 0.54 18 B(4-16)09bda 0.45 534 7.2 25 6.2 140 2.9 110 120 146 0 9.3 30 8.2 91.2 0.79 19 B(4-16)13dbb 0.20 458 7.9 17 5.3 130 2.7 99 100 120 0 2.8 27 5.4 91.8 1.04 20 B(4-16)15abc 0.17 458 8.2 12 1.1 150 1.6 1 10 120 56 0 7.9 13 6.5 98.0 1.00 21 B(4-16)18dcb 4.4 643 7.4 89 13.0 93 4.1 43 250 184 0 0.9 34 22.6 77.5 -1.79 22 B(5-15)30ddb2 868 7.6 53 24.0 200 7.6 150 310 186 0 1.2 22 80.0 -0.92 23 B(5-15)06baal 1.9 1750 7.6 81 17.0 480 7.6 340 650 100 0 6.5 10.7 92.9 -1.43 24 B(5-15)21baa 0.47 820 7.7 22 6.5 260 9.1 210 180 168 0 6.8 9.8 93.6 2.11 25 B(5-16)09bcc 1.2 806 7.6 42 6.5 230 3.7 230 200 74 0 5.2 32 13.1 94.1 -0.32 26 B(5-16)10dca 0.67 569 8.0 18 1.5 170 2.8 120 160 90 0 6.9 17.0 97.4 0.80 27 B(5-16)27bad 0.85 674 7.8 39 5.1 190 4.2 190 140 110 0 4.4 10.0 94.0 0.28 28 B(6-15)07aac 1.4 596 7.8 42 11.0 140 5.8 130 150 144 0 3.8 32 15.3 85.2 -0.15 29 B(6-15)08caa 716 7.7 49 14.0 170 7.2 170 200 128 0 4.4 31 84.7 -0.87 30 B(6-15)33bab 1.1 844 7.6 39 9.7 240 7.4 210 200 150 0 0.5 36 12.9 91.4 0.89 31 B(6-16)13dac 2.6 915 7.7 75 9.7 210 8.0 220 290 128 0 3.3 30 15.9 90.1 -2.55 32 B(6-16)17baa 2.2 1110 7.7 60 6.4 300 5.9 250 410 71 0 4.8 25 16.8 95.1 -2.16 33 B(6-16)17bda 1050 7.8 45 3.4 310 6.3 220 380 67 0 6.1 96.8 -0.35 34 B(6-16)22ada 1640 7.8 110 23.0 420 12.0 310 660 98 0 4.7 89.3 -3.07 35 B(6-16)23ddc 4260 7.7 340 80.0 950 12.0 800 1900 121 0 4.5 85.7 -17.58 36 B(6-16)25bbc 4.1 1280 7.6 76 15.0 340 8.7 280 430 122 0 4.8 24.7 91.0 -1.29 37 B(6-16)32bbc 1.3 588 7.7 21 1.8 170 2.5 120 170 84 0 6.3 34 28.3 97.2 0.60 38 B(6-16)33aaa 1.0 782 8.0 54 1.1 230 3.0 150 250 72 0 7.1 8.5 98.4 0.68 39 B(6-16)33aad 865 8.0 35 2.5 240 3.3 170 340 58 0 7.6 97.3 -1.26 40 B(6-17)12dbb2 4.0 477 7.4 62 8.8 85 2.3 81 7 296 0 0.8 37 29.5 82.5 1.65 41 B(7-17)23cdc2 2.2 800 7.4 62 12.0 220 7.0 210 150 170 0 4.2 34 16.2 89.1 1.14 42 B(7-17)35bcc 1.7 869 7.8 48 3.2 240 4.6 180 320 70 0 5.0 21 16.2 96.5 -1.07
AVERAGE 1.25 898 7.8 54 8.0 236 4.9 188 283 119 0 2 4.5 29 12.0 92.5 -0.52 STD DEV 1.3 626 0.3 63 12.6 141 2.6 121 307 53 0.7 2.8 6 7.6 5.1 3.69
MINIMUM 0.060 275 7.2 4.2 0.4 85 1.1 32 7 42 0 0.5 13 3.2 77.5 -17.58 MAXIMUM 4.4 4260 8.4 340 80.0 950 12.0 800 1900 296 3 9.7 37 29.5 98.9 3 • 94
(a) + + 2+ - 2- M - Na + K + 2 Mg - Cl -2 SO 4 60
Table 2. Well construction details.
Well State Well Perforated Casing (a) Number Well Depth Interval Diameter Available Number (feet) (feet) (inches) Well Logs 1 B(2-13)19ccc 8 2 B(2-14)10cdc 455 340-380 8 D,L 3 B(2-14)28ccc 350 75-253 8 D,L 4 B(3-14)09ddd 5 B(3-14)13add 6 B(3-15)02dac 7 B(3-15)02dab 960 20 L 8 B(3-15)23bdb2 500 300-500 8 D 9 B(4-14)04aac 652 577-652 6 10 B(4-14)18cdd 11 B(4-14)29cdd 12 B(4-15)08acc2 6 13 B(4-15)09ada 230 6 14 B(4-15)09bad 250 - 6 15 B(4-15)18bbb 1005 0-1005 20 D 16 B(4-15)18bbc 1242 300-1100 9 17 B(4-15)28bbd 20 D 18 B(4-16)09bda - - 8 19 B(4-16)13dbb 285 20 B(4-16)15abc 303 21 B(4-16)18dcb 600 400-600 D 22 B(5-15)30ddb2 - 23 B(5-15)06baal 1165 220-910 20 D 24 B(5-15)21baa 250 6 25 B(5-16)09bcc 145 6 26 B(5-16)10dca 655 260-480 16 D 27 B(5-16)27bad 750 D 28 B(6-15)07aac 1000 500-1000 16 29 B(6-15)08caa - 30 B(6-15)33bab 422 - 31 B(6-16)13dac 1000 500-1000 16 32 B(6-16)17baa 550 - 20 33 B(6-16)17bda 510 50-510 34 B(6-16)22ada 800 250-794 20 D 35 B(6-16)23ddc 1100 190-1000 20 36 B(6-16)25bbc 1000 500-1000 16 37 B(6-16)32bbc 900 38 B(6-16)33aaa 700 235-700 20 D 39 B(6-16)33aad - 40 B(6-17)12dbb2 200 140-200 8 41 B(7-17)23cdc2 930 180-200 8 42 B(7-17)35bcc -
(a) D - Driller's Log L - Lithologic Log 61
(.4thl --_,/ 01== Si
SCALE IN MILES Well Number (State Well Numbers Provided on Table 1)
Figure 9. Well location map. 62 saturation index for that mineral is close to 0. The saturation index is less than zero when the sample is undersaturated and greater than zero when the sample is oversaturated. The WATEQF program also calcu- lates carbon dioxide gas partial pressures and log activity molar ratios needed for mineral stability diagrams.
General Mineral Hydrochemistry
This section discusses the occurrence and distribution of the major dissolved ions in the groundwater of the Ranegras Plain basin.
Total Dissolved Solids
The total dissolved solids (TDS) concentrations listed in
Table 1 represent the sum of the concentrations of all measured dissolv- ed constituents in each groundwater sample. The TDS of groundwater in the Ranegras Plain basin ranges from a low of 275 mg/1 on the east side of the basin near the town of Hope (Well No. 9) to a high of 4260 mg/1 in the north-central part of the basin (Well No. 35) [Table 1,
Figure 10].
Samples from wells in the southern half of the basin and the eastern and western margins of the northern half of the basin contain from 500 to 100 mg/1 TDS, whereas samples from those wells located along the basin axis in the northern half of the basin generally contain from
1000 to over 1700 mg/1 TDS. Water from Well No. 35 contains 4260 mg/1
TDS, apparently due in large part to the dissolution of gypsum as shown by the high calcium (340 mg/1) and sulfate (1900 mg/1) concentrations. 63
acto
869.
477 596. • 716 1050 :1 1 1 50-Ç500 • 915 1640 2 "- '1000-200 554 782• 1280 865 • \ 1750
250-500 •793
SCALE IN MILES
Figure 10. Total dissolved solids concentrations in groundwater. 64
The lowest TDS concentrations occur in Bear Valley and near the town of Hope on the west and east sides of the basin. Groundwater recharge occurs at these two locations due to the infiltration of sur- face water in washes.
Relationship of Well Depth and Water Quality
Few data are available to compare the groundwater quality and well depth in the Ranegras Plain basin. In general, high capacity wells in the basin center must be completed much deeper than wells at the basin perimeter to produce approximately 1000 gallons per minute (gpm) or more. These deep central wells obtain water from high TDS zones.
The groundwater chemistry for samples from two pairs of nearby wells with markedly different mineral content are compared later in this chapter (Wells No. 15 and 16, Wells No. 35 and 36).
Water Type
The groundwater in the Ranegras Plain basin is predominantly the sodium chloride-sulfate chemical type. Table 3 lists the concentrations of the major ions in groundwater in moles per liter and milliequivalents per liter (meq/l) to demonstrate the relative molar and equivalent per- centages of each constituent. Stiff diagrams for the wells included in this study are shown in Figure 11. Groundwater samples from recharge areas are sodium bicarbonate (Well No. 9), sodium chloride-bicarbonate
(Well No. 4), or sodium-calcium bicarbonate (Well No. 40). Well No. 15 is predominantly calcium-sulfate type due to gypsum bearing sediments in the lower perforated interval of this well. 65
Table 3. Major ion content of groundwater samples.
Milligrams per Liter Moles per Liter Milliequivalents per Liter
Mean Minimum Maximum Mean Minimum Maximum Mean Minimum Maximum
Calcium 54 4.2 340 1.35 0.10 8.48 2.69 0.21 16.97 Magnesim 8.0 0.4 80 0.33 0.02 3.29 0.66 0.03 6.58 Sodium 236 85 950 10.27 3.70 41.32 10.27 3.70 41.32 Potassium 4.9 1.1 12 0.13 0.03 0.31 0.13 0.03 0.31
Chloride 188 32 800 5.30 0.90 22.57 5.30 0.90 22.57
Sulfate 283 6.8 1900 2.95 0.07 19.78 5.89 0.14 39.56
Bicarbonate 119 42 296 1.95 0.69 4.85 1.95 0.69 4.85
Carbonate 0 0 3 0.00 0.00 0.05 0.00 0.00 0.10
Fluoride 5.3 0.5 12 0.28 0.03 0.63 0.28 0.03 0.63 Silica 29 13 37 1.03 0.46 1.32 1.03 0.46 1.32 66
(
SCALE IN MILES
Na+K CI CA77K HCO3 80 Mg 4 -20-10 0 10 20 s ; 50 mectiinch R Well Is Located in Recharge Zone
Figure 11. Stiff diagram map. 67
p_Li
The pH of groundwater in the southern half of the basin gener-
ally ranges from 8.2 to 8.4 (Table 1, Figure 12). Groundwater closer to
the basin margins has lower pH values indicative of recently recharged
water. Groundwater in the northern half of the basin ranges from pH 7.6
to 7.8, considerably lower than the southern half of the basin. These
lower pH values may be due to a greater influx of recharged water into
the northern half of the basin (Robertson, personal communication, 1987).
pH increases during the weathering of silicate minerals, as discussed
later in this chapter. The longer retention time of groundwater in the
southern half of the basin would allow the groundwater to reach higher
pH values.
Sodium
Sodium is the dominant cation in the groundwater of the Ranegras
Plain basin. The sodium percent (equivalents of sodium per total equiv-
alents of sodium, calcium, potassium, and magnesium) averages 74 percent
and ranges from 42 percent (Well No. 21) to 96 percent (Well No. 7)
[Table 1]. The sodium concentration in groundwater ranges from a low of
85 to 95 mg/1 in recharge areas in Bear Valley (Well No. 21), near Pyra- mid Peak (Well No. 9), and adjacent to Bouse Wash (Well No. 35), to a high of 950 mg/1 in the north central part of the basin (Well No. 35)
[Figure 13]. The highest sodium concentrations are along the basin axis
in the northern half of the basin. 68
, 7.8-8.0
7.4 7.2-7.4
7.2-7.
8.0-8.2
SCALE IN MILES
•8.1 pH of groundwater Well is located in recharge zone
Figure 12. pH of groundwater. 69
01TT4 SCALE IN MILES
Figure 13. Sodium concentrations in groundwater. 70
Saline water associated with evaporite deposits appears to be the source of the majority of the sodium in the groundwater as shown by the associated elevated concentrations of chloride and sulfate.
Calcium
Calcium concentrations in groundwater range from 4 mg/1 in Well
No. 9 to 340 mg/1 in Well No. 35 (Figure 14). Groundwater in the south- ern half of the basin contains calcium concentrations generally between
5 and 12 mg/1, although the calcium concentrations at the southern basin perimeter are between 40 and 100 mg/1 (Wells No. 3 and 5).
Groundwater in the northern half of the basin contains 25 to 50 mg/1 calcium around the basin perimeter, and 50 to 340 mg/1 in the basin center. The high calcium concentrations correlate with elevated sulfate, chloride, and sodium concentrations, and appear to be due to evaporite deposits.
Magnesium
Magnesium concentrations average 8 mg/1 and range from less than
1 mg/1 to 80 mg/1 (Table 1, Figure 15). The lowest concentrations occur on the east side of the basin, directly west of Pyramid Peak, which is composed of Tertiary basalt. The highest concentrations occur in the northwest corner of the basin in an area surrounded by Mesozoic metamor- phic rocks and Late Cretaceous granite. The elevated levels of magne- sium in this area may be due to the alteration of magnesium olivine according to the following equation (Hem, 1970):
5 Mg2 SiO4 + 8 H 2 H 20 = Mg6 (OH) 8 Si40 10 + 4 Mg H4 SiO4 77_
Figure 14. Calcium concentrations in groundwater. 72
SCALE IN MILES 5
• Magnesium 6 . 3 Concentration (mg/I)
Figure 15. Magnesium concentrations in groundwater. 73
Olivine was described in the lithologic log for Well No. 41 (Appendix A).
Groundwater from Well No. 35, which has the highest total dis- solved solids content of any in the basin, contains 80 mg/1 magnesium.
This anomalous value may be attributed to evaporites.
Potassium
Potassium concentrations range from 1.1 mg/1 in Well No. 6 to
12 mg/1 in Wells No. 34 and 35 (Table 1, Figure 16). The majority of samples in the basin contain between 2 and 5 mg/1 potassium. The high- est concentrations (generally 5-10 mg/1) are in the northeast quadrant and southeast corner of the basin. Potential potassium sources in those areas include potassium feldspar and biotite, which are major components of the granite found in the Bouse Hills and Granite Wash Mountains and the Mesozoic metamorphic rocks found in the southern end of the basin.
Absorption of potassium on clays formed from the weathering of these rocks is the most likely geochemical control for potassium. Potassium correlates poorly with calcium, sodium, chloride, and sulfate, and, therefore, does not appear to be associated with the evaporite deposits.
Chloride
Average chloride concentrations for the Ranegras Plain basin represent 52 percent of the total molar anion concentrations and 40 percent of the total anion concentrations in meq/1. The mean chloride concentration, 188 mg/1, (5.30 moles per liter), represents approxi- mately half of the major anion molar content (Table 3). The majority of groundwater contains between 100 and 250 mg/1 chloride (Figure 17). The 74
Figure 16. Potassium concentrations in groundwater. 75
• 1 5Q 280 • • 120 170 210
190 • 100-250
110 290 290
SCALE IN MILES
. Chloride 180 Concentration (mg/I)
Figure 17. Chloride concentrations in groundwater. 76 lowest concentrations occur in recharge areas in the central west and east parts of the basin (Wells No. 9 and 21). The highest concentra- tions occur in the northern half of the basin along the basin axis.
Chloride concentrations correlate with those areas of high TDS, calcium, sodium, and sulfate, thus indicating an association with evaporite deposits.
Chloride accumulations are common in sediments deposited in closed basins. Igneous rocks generally yield only small concentrations of chloride to groundwater; generally the most important sources are associated with sedimentary rocks, particularly the evaporites (Hem,
1970). The limestones and gypsum deposits in the Plomosa Mountains and
Granite Wash Mountains or hydrothermal solutions may have served as the chloride source.
Sulfate
Sulfate represents 45 percent of the total milliequivalents of major anions (based on chloride, sulfate, and bicarbonate, and carbon- ate) for the average basin water quality (Table 3). Concentrations range from 6.8 mg/1 in Well No. 40, a recharge well adjacent to Bouse
Wash in the northern part of the basin, to 1900 mg/1 in Well No. 35, the most mineralized well in the basin (Table 1, Figure 18). The mean con- centration is 283 mg/l. Groundwater in the southern half of the basin and the perimeter of the northern half of the basin contains between 100 and 250 mg/1 sulfate. Sulfate concentrations are greatest in the north- central part of the basin and correlate positively with TDS, calcium, sodium, and chloride. 77
n 200 fr;\4"
150 • 20 100-250 • 200 6.8 • 150 • 6410 0 290. 0 380 . 001 0 0 0 - 2 006
‘,) 250 60 430 • 034 ° 170 • 200 250-500: 650 - 500-1000 • 160• 200
• 310 / * 4 0-100
• 110 100-250
CQ" 130 180
SCALE IN MILES
• Sulfate 160 concentraflon (mg/0
Figure 18. Sulfate concentrations in groundwater. 78
Evaporite deposits containing gypsum appear to be the primary source of sulfate in the basin, but the oxidation of pyrite or other sulfide minerals may be an additional source. Gypsum deposits are in
Permian limestone beds in the Plomosa Mountains and Granite Wash Moun- tains and have been mined for local agricultural use (Keith, 1978).
Bicarbonate and Carbonate
Bicarbonate concentrations range from 42 mg/1 in the basin cen- ter (Wells No. 13 and 14) to 296 mg/1 in Well No. 40 (Table 1,
Figure 19). The highest bicarbonate concentrations occur in potential recharge areas along the basin perimeter (Wells No. 5, 9, 18, and 30) or along Bouse Wash and its tributaries (Wells No. 4, 22, and 40).
Groundwater samples from the basin center have significantly lower bicarbonate concentrations than the remainder of the basin. This condition may be due to calcium carbonate precipitation within the aqui- fer or to the mixing low TDS groundwater with high sulfate groundwater.
As rainfall saturated with atmospheric carbon dioxide infiltrates, addi- tional CO 2 is added by high soil CO 2 concentrations. Hydrogen ions are consumed by the incongruent dissolution of silicate minerals as the recharged groundwater moves through the aquifer. The rise in pH results in the precipitation of calcite, thereby removing dissolved inorganic carbon from the aqueous phase. The concentration of bicarbonate there- fore decreases as the groundwater moves from recharge to discharge locations.
Mixing of the low-TDS, high-bicarbonate recharge water with the deeper, more saline waters sampled by the centrally located wells may 79
=n=n SCALE IN MILES
• Bicarbonate 58 Concentration (mgiO
Figure 19. Bicarbonate concentrations in groundwater. 80
also lower the dissolved inorganic carbon concentration. Elevated cal-
cium concentrations from gypsum dissolution may oversaturate the ground-
water with respect to calcite and result in calcite precipitation within
the aquifer or the pumped groundwater.
Groundwater samples from only three wells in the Ranegras Plain
have sufficiently high pH (greater than 8.3) to contain aqueous carbon-
ate concentrations above 1 mg/l.
Fluoride
Fluoride concentrations in the Ranegras Plain basin average 5.3
mg/1 and range from less than 1 mg/1 at the basin perimeter to 12 mg/1
in the south central part of the basin (Table 1, Figure 20). Over 80
percent of the well samples in the basin contain fluoride concentrations
exceeding 2 mg/1; therefore, the majority of the groundwater is not
suitable for drinking. Groundwater in the north central and south cen-
tral parts of the basin contain from 5 to 8 mg/1 and 8 to 12 mg/1,
respectively.
The elevated fluoride concentrations are due to the presence of
fluorite (CaF2 ) in the basin sediments. Robertson (1985) demonstrated that groundwaters in the Ranegras Plain basin are saturated with respect
to fluorite, and that conclusion is supported by the data in this thesis,
as discussed in the section in this chapter on mineral saturation indi-
ces. Fluorite was previously mined in the Plomosa Mountains. Barite
and fluorite are common gangue minerals in metallic deposits in the
Plomosa Mountains, and occur in fissure veins in metamorphosed sediments 81
3.6 7.9 •. 5• 3 0.9 2.8 0. •
SCALE IN MILES
Figure 20. Fluoride concentrations in groundwater. 82 north of Bouse, in the andesitic volcanics to the east of Bouse, and in
the Granite Wash Mountains (Keith, 1978).
Groundwater Recharge
Six of the wells in the Ranegras Plain basin are in recharge zones as shown by the chemically distinct content of groundwaters at those locations compared to the rest of the basin. Samples from Wells
No. 3, 4, 5, 9, 21, and 40 have relatively low pH, high bicarbonate concentrations, and generally lower sodium percent (equivalents of so- dium per total equivalents of sodium, calcium, magnesium, and potassium) than other wells in the basin (Table 1, Figure 11). These wells are either at the base of the hills bordering the groundwater basin (Wells
No. 3, 5, 9, and 21) or adjacent to washes where infiltration occurs during times of flow (Wells No. 4 and 40). Samples from Wells No. 9,
21, and 40 contain significantly lower total dissolved solids than sur- rounding wells in the vicinity.
Groundwater from Well No. 4 has a relatively low pH (7.2) and high bicarbonate concentration (232 mg/1), but a high sodium percent
(92.3). This well therefore may represent a mixture of recently recharged water and older groundwater.
Water from Well No. 8 contains a high bicarbonate concentration relative to the other anions in solution, but the sodium percent (92.5) and pH (8.1) are higher than the other recharge wells. Water from this well may also represent a mixture of recently recharged and older waters. 83
Mineral Saturation Indices
Table 4 summarizes mineral saturation indices calculated by the
WATEQF program for selected minerals of interest to the hydrogeochemis- try of the Ranegras Plain basin. Saturation indices are compiled for the aluminohydroxide minerals, clays, silicate minerals, carbonates, sulfates, and fluorite for each of the 42 well samples. Only 12 of the
42 well samples from the Ranegras Plain basin were analyzed for alumin- um, therefore calculated saturation indices for the phyllosilicates and aluminohydroxides are available only for these 12 wells samples.
The inaccuracy of dissolved aluminum analyses may create large errors in the calculated saturation indices of the aluminosilicate min- erals (Jones and Swellinger, 1974). Therefore, the saturation indices for those minerals are considered approximate. WATEQF computes ratios of ion activities useful for plotting mineral stability diagrams for the aluminosilicate minerals. Saturation indices have been calculated for calcium montmorillonite, in addition to the montmorillonite composition proposed by Belle Fourche (Kittrick, 1971a) and Aberdeen (Kittrick,
1971b).
The saturation index (S.I.) for each mineral averaged for all groundwater samples in the basin were grouped into three categories:
(1) undersaturated (S.I. < -0.2), (2) approximately saturated (-0.2 >
S.I. > 0.2), and (3) oversaturated (S.I. > 0.2). The groundwater is approximately saturated with respect to calcite, illite, chalcedony, barite, and fluorite. The groundwater is undersaturated with respect to gibbsite, halloysite, adularia, albite, anorthite, analcime, chlorite, 84
Table 4. Hineral saturation indices.
ALUMINO- CLAYS SILICATE MINERALS HYDROXIDES Well State Well pC0 Clino- Number Number 2 Gibbsite Diaspora Illite Kaolinite Ca Mont. Mont. BF Mont. AB Halloysite Chlorite Adularia Albite Anorthite Analcime K-Mica enstatite Diopside 1 B(2-13)19ccc 5.19E-04 -0.958 0.968 -0.214 -0.031 -0.261 4.733 4.275 -4.058 1.452 0.103 -0.728 -3.807 -2.678 -1.665 -1.767 -0.488 2 B(2-14)10cdc 6.24E-04 -1.974 -0.735 3 B(2-14)28ccc 1.68E-03 -1.701 -0.740 4 B(3-14)09ddd 1.84E-03 -2.157 -1.624 5 B(3-14)13add 1.19E-02 0.071 2.006 0.578 1.845 1.596 4.924 3.917 -2.161 -5.223 -0.533 -1.264 -3.144 -3.102 -2.170 -3.539 -3.667 6 B(3-15)02dac 4.42E-04 -2.976 -2.294 7 B(3-15)02dab 4.54E-04 -2.227 -1.076 8 B(3-15)23bdb2 5.98E-04 -1.897 -1.097 9 B(4-14)04aac 1.23E-03 -0.600 1.322 -1.263 0.015 -0.802 3.142 2.471 -4.022 -4.753 -1.216 -1.969 -4.684 -3.594 -2.281 -3.292 -3.219 10 B(4-14)18cdd 6.69E-04 -2.849 -2.161 11 B(4-14)29cdd 5.56E-04 -2.541 -1.791 12 B(4-15)08acc2 4.36E-03 -3.692 -3.454 13 B(4-15)09ada 7.67E-04 14 B(4-15)09bad 6.23E-04 -3.396 -2.548 15 B(4-15)18bbb 1.06E-03 -0.206 1.712 0.582 1.439 1.401 4.845 4.016 -2.609 -3.615 -0.107 -0.735 -2.599 -2.689 -0.396 -3.101 -1.997 16 B(4-15)18bbc 6.27E-04 -4.042 -4.032 17 B(4-15)28bbd 3.88E-04 -2.248 -1.114 18 B(4-16)09bda 9.30E-03 -3.865 -4.627 19 B(4-16)13dbb 1.24E-03 0.522 2.409 2.259 2.855 2.869 5.249 4.495 -1.270 -0.899 0.582 -0.111 -2.410 -2.120 1.654 -2.146 -1.190 20 B(4-16)15abc 3.50E-04 -0.659 1.259 -1.674 -0.270 -1.153 -4.317 -3.102 -1.665 -1.984 -4.454 -3.536 -2.860 -2.977 -2.421 21 B(4-16)18dcb 7.57E-03 -0.038 1.893 0.820 1.779 1.668 5.051 4.156 -2.237 -2.813 -0.234 -1.133 -2.932 -3.058 -0.149 -2.989 -2.712 22 B(5-15)30ddb2 7.93E-03 -2.805 -2.892 23 B(5-15)06baal 2.36E-03 -2.664 -2.169 24 B(5-15)21baa 3.41E-03 -2.607 -2.230 25 B(5-16)09bcc 1.85E-03 -3.032 -2.771 26 B(5-16)10dca 1.00E-03 -0.853 1.099 -1.222 -0.177 -0.703 -4.141 -2.297 -1.094 -1.509 -3.918 -3.220 -2.575 -2.597 -1.767 27 B(5-16)27bad 1.24E-03 -4.370 -4.743 28 B(6-15)07aac 2.22E-03 -0.212 1.699 0.905 1.445 1.336 -2.619 -0.468 0.164 -0.762 -3.158 -2.740 -0.157 -2.474 -1.846 29 B(6-15)08caa 2.52E-03 -2.533 -2.032 30 B(6-15)33bab 3.66E-03 -2.879 -2.648 31 B(6-16)13dac 2.48E-03 -2.739 -2.103 32 B(6-16)17baa 1.36E-03 -3.033 -2.609 33 B(6-16)17bda 1.03E-03 -3.114 -2.630 34 B(6-16)22ada 1.45E-03 -0.325 1.595 0.198 0.826 0.411 4.673 4.084 -3.217 0.072 -0.254 -0.990 -3.339 -2.751 -0.774 -2.388 -1.624 35 B(6-16)23ddc 1.51E-03 -3.673 -3.626 36 B(6-16)25bbc 3.08E-03 -2.646 -2.168 37 B(6-16)32bbc 1.78E-03 -0.370 1.565 0.030 1.094 0.864 5.014 4.199 -2.911 -4.433 -0.505 -0.917 -3.525 -2.821 -1.072 -3.179 -2.871 38 B(6-16)33aaa 5.55E-04 -3.214 -2.248 39 B(6-16)33aad 6.98E-04 -2.762 -1.888 40 B(6-17)12dbb2 1.13E-02 -3,377 -3.335 41 B(7-17)23cdc2 6.41E-03 -3.296 -3.331 42 B(7-17)35bcc 1.10E-03 -0.356 1.568 -0.325 0.743 0.264 4.148 3.368 -3.289 -3.618 -0.710 -1.264 -3.599 -3.004 -1.280 -3.111 -2.587 AVERAGE 2.52E-03 -0.306 1.469 0.056 0.964 0.624 4.642 3.887 -3.071 -2.475 -0.456 -1.114 -3.464 -2.943 -1.144 -2.875 -2.368 STD DEV 2.93E-03 0.388 0.562 1.053 0.925 1.160 0.605 0.579 0.906 2.003 0.613 0.514 0.656 0.387 1.229 0.601 0.982 MINIMUM 3.50E-04 -0.958 0.000 -1.674 -0.270 -1.153 3.142 2.471 -4.317 -5.223 -1.665 -1.984 -4.684 -3.594 -2.860 -4.370 -4.743 MAXIMUM 1.19E-02 0.522 2.409 2.259 2.855 2.869 5.249 4.495 -1.270 1.452 0.582 -0.111 -2.410 -2.120 1.654 -1.701 -0.488 85
Table 4, Continued
CARBONATES SULFATES Well State Well Stron- Number Number Calcite Aragonite Dolomite tianite Magnesite Witherite Gypsum Anhydrite Barite Celestite Fluorite
1 B(2-13)19ccc -0.016 -0.135 -0.315 -1.536 -0.784 -3.366 -2.000 -2.153 -0.371 -2.635 0.144 2 B(2-14)10cdc 0.025 -0.094 -0.400 -1.589 -0.910 -3.419 -2.347 -2.500 -0.813 -3.077 0.216 3 B(2-14)28ccc 0.228 0.109 0.559 -0.998 -0.154 -3.272 -1.480 -1.632 -0.001 -1.821 -1.608 4 B(3-14)09ddd -0.164 -0.282 -0.240 -1.681 -0.564 -3.429 -2.282 -2.444 -0.563 -2.922 0.201 5 B(3-14)13add -0.029 -0.152 -0.735 -1.412 -1.185 -3.836 -1.081 -1.215 0.079 -1.563 0.100 6 B(3-15)02dac -0.513 -0.640 -1.979 -1.938 -2.244 -2.358 0.374 7 B(3-15)02dab -0.096 -0.230 -0.907 -1.451 -1.273 -3.166 -1.949 -2.041 -0.072 -2.365 0.370 8 B(3-15)23bdb2 -0.027 -0.146 0.014 -1.731 -0.444 -3.487 -2.077 -2.229 -0.559 -2.896 -0.269 9 B(4-14)04aac -0.484 -0.602 -1.554 -1.248 -1.558 -3.536 -2.774 -2.936 -0.841 -2.661 -1.969 10 B(4-14)18cdd -0.149 -0.268 -1.071 -1.507 -1.407 -3.160 -2.189 -2.342 -0.222 -2.662 0.356 11 B(4-14)29cdd -0.218 -0.336 -0.950 -1.684 -1.219 -2.433 -2.595 -0.566 -3.022 0.034 12 B(4-15)08acc2 -0.157 -0.273 -1.440 -1.633 -1.775 -3.801 -1.337 -1.518 0.016 -1.950 0.533 13 B(4-15)09ada -0.256 -0.372 -1.622 -1.858 0.531 14 B(4-15)09bad -0.255 -0.371 -1.956 -2.191 -0.896 -1.072 0.498 15 B(4-15)18bbb 0.192 0.075 -1.030 -1.079 -1.711 -3.951 -0.235 -0.407 0.613 -0.626 0.698 16 B(4-15)18bbc -0.537 -0.754 -2.161 -2.053 -1.491 -1.984 0.724 17 B(4-15)28bbd -0.164 -0.279 -0.893 -1.709 -1.223 -3.439 -1.668 -1.859 0.060 -2.357 -1.841 18 B(4-16)09bda -0.701 -0.818 -1.714 -1.984 -1.503 -3.809 -1.708 -1.880 0.175 -2.121 0.748 19 B(4-16)13dbb -0.385 -0.502 -1.031 -1.827 -1.144 -3.503 -1.955 -2.148 0.021 -2.522 -0.348 20 B(4-16)15abc -0.435 -0.551 -1.612 -1.819 -1.667 -3.619 -1.988 -2.160 -0.182 -2.503 0.313 21 B(4-16)18dcb 0.133 0.012 -0.251 -0.699 -0.865 -3.743 -0.959 -1.102 0.138 -0.898 -0.843 22 B(5-15)30ddb2 -0.082 -0.209 -0.178 -0.568 -1.138 -1.253 -0.903 23 B(5-15)06baal -0.169 -0.285 -0.706 -1.270 -1.027 -3.817 -0.782 -0.953 0.561 -1.012 0.701 24 B(5-15)21baa -0.223 -0.342 -0.666 -1.430 -0.928 -3.501 -1.669 -1.822 0.031 -1.992 0.335 25 B(5-16)09bcc -0.419 -0.537 -1.346 -1.494 -1.415 -3.968 -1.350 -1.517 0.088 -1.552 0.400 26 B(5-16)10dca -0.167 -0.299 -1.089 -1.168 -1.386 -3.407 -1.749 -1.846 -0.040 -1.815 0.247 27 B(5-16)27bad -0.483 -0.699 -1.996 -1.642 -1.942 -3.756 -1.436 -1.929 0.624 -1.838 0.715 28 B(6-15)07aac 0.071 -0.044 -0.148 -0.931 -0.712 -3.341 -1.428 -1.614 0.160 -1.571 0.182 29 B(6-15)08caa- -0.019 -0.136 -0.281 -0.752 -1.283 -1.455 0.322 30 B(6-15)33bab -0.171 -0.287 -0.649 -1.242 -0.969 -3.675 -1.389 -1.571 0.104 -1.598 -1.660 31 B(6-16)13dac 0.123 0.006 -0.339 -0.848 -0.951 -3.657 -1.003 -1.174 0.209 -1.104 0.214 32 B(6-16)17baa -0.270 -0.387 -1.206 -1.197 1.425 -4.410 -0.989 -1.161 -0.138 -1.046 0.405 33 B(6-16)17bda -0.304 -0.421 -1.422 -1.607 -1.124 -1.291 0.499 34 B(6-16)22ada 0.159 0.042 -0.048 -0.696 -0.651 -0.817 0.541 35 B(6-16)23ddc 0.040 -0.176 -0.674 -1.144 0.070 -0.421 1.252 36 B(6-16)25bbc 0.001 -0.120 -0.380 -0.780 -0.862 -3.670 -0.913 -1.051 0.387 -0.797 0.436 37 B(6-16)32bbc -0.481 -0.604 -1.714 -1.236 -1.712 -3.629 -1.655 -1.788 0.166 -1.509 0.274 38 B(6-16)33aaa -0.079 -0.196 -1.546 -1.306 -1.956 -3.700 -1.060 -1.231 0.310 -1.418 0.745 39 B(6-16)33aad -0.139 -0.256 -1.124 -1.474 -1.334 -1.506 0.649 40 B(6-17)12dbb2 0.178 0.063 -0.224 -0.564 -0.898 -1.118 -2.547 -2.758 1.175 -2.447 -0.912 41 B(7-17)23cdc2 -0.129 -0.244 -0.692 -1.106 -1.507 -4.010 -1.312 -1.512 -0.181 -1.439 0.424 42 B(7-17)35bcc -0.215 -0.334 -1.295 -1.173 -1.566 -3.977 -1.135 -1.292 0.085 -1.212 0.374
AVERAGE -0.162 -0.287 -0.929 -1.343 -1.192 -3.148 -1.487 -1.672 0.014 -1.847 0.100 STD DEV 0.220 0.227 0.642 0.347 0.628 1.232 0.607 0.591 0.414 0.758 0.742
MINIMUM -0.701 -0.818 -2.161 -1.984 -2.191 -4.410 -2.774 -2.936 -0.841 -3.077 -1.969 MAXIMUM 0.228 0.109 0.559 -0.564 1.425 0.000 0.070 -0.407 1.175 0.000 1.252 86
K-mica, clinoenstatite, diopside, dolomite, strontianite, magnesite, witherite, gypsum, anhydrite, and celestite. The basin average ground- water is only slightly undersaturated with respect to aragonite (S.I. —
-0.287); groundwater samples from 15 wells are saturated with respect to aragonite. Two wells (No. 3 and 8) are saturated with respect to dolo- mite. Water from one well (No. 35) is saturated with respect to gypsum.
Groundwater is oversaturated with respect to diaspore, kaolinite, cal- cium montmorillonite, Belle Fourche montmorillonite (Kittrick, 1971a), and Aberdeen montmorillonite (Kittrick, 1971b).
These data indicate that carbonate equilibrium is a dominant factor controlling the hydrogeochemistry of the Ranegras Plain ground- water basin. Dissolved barium and fluoride appear to be controlled by the solubility of barite and fluorite.
The silicate minerals, with the exception of the clays, are undersaturated by one to four orders of magnitude. This indicates the that the potential exists for the silicate minerals to react with groundwater and release dissolved constituents through incongruent dis- solution. Clay minerals account for the majority of the sediments in the alluvial basins of southern Arizona, and are the dominant minerals controlling groundwater chemistry in some basins.
Weathering of Silicate Minerals
The weathering of silicate minerals is a significant contribut- ing factor to the hydrogeochemistry of the Ranegras Plain basin. Sili- cate mineral hydrolysis is demonstrated by mineral saturation indices, mineral stability diagrams, the high dissolved silica concentrations in 87 groundwater, elevated pH values, and the decrease of dissolved inorganic carbon in groundwater downgradient from recharge areas.
Mineral stability diagrams prepared from the Ranegras Plain groundwater analyses (Figures 21 to 25) display linear groupings of data points indicating that the weathering of silicate minerals and reactions of clay minerals may be a controlling factor in the groundwater chemistry of the basin. The presence of many different minerals and rock types in the aquifer sediments, and variation of the partial pressure of carbon dioxide (pCO 2 ), dissolved silica concentration, and temperature in the basin complicates the interpretation of these mineral stability diagrams. Therefore mineral phase boundaries have not been shown on these mineral stability diagrams.
Kaolinite and montmorillonite are the clay minerals expected to be formed in the environment of the Ranegras Plain groundwater basin.
Groundwater with a silica to aluminum molar ration (Si/A1 ratio) near 2, a low cation content, and a pH less than approximately 7 favors the formation of kaolinite and halloysite (Birkeland, 1974). Higher pH values increase the saturation with respect to these minerals. Montmo- rillonite forms under the conditions of a Si/A1 ratio greater than 2, neutral to alkaline pH, and relatively high concentrations of calcium, magnesium, and sodium. Illite forms under the same conditions when the concentration of potassium is high. The approximate saturation of Rane- gras Plain groundwater with respect to illite suggests that the forma- tion of illite or an illite-montmorillonite mixed layer mineral may be a factor controlling the potassium concentration in the groundwater. 88
3.0 —
7.0 —
/•••n (1:2 • • +al 6.0 —
caz Li, • oCS) • •
5.0 — • fe
4.0 —6.0 0 log a H4SiO4
Figure 21. Log[Na]/[H] versus log [H4SiO4 ].
14.0 —
150 — • •• • •
Ncri-2
120 — co O. •
o
11.0 —
10.0 - 0 log , H a 4 4
Figure 22. Log[Ca 2± ]/[11+ ] 2 versus log [H4 SiO 4 ].
89
13 0 —
•
•
11.0 —
10.0 3.00 4.80 5.80 6.80 7.00
log (a Na+ /a iii )
Figure 23. Log[Ca 2+ ]/[1-11 ] 2 versus log [Nall/[1-1-4- ].
14.0 —
13.0 — • • • al • s. •
• I a: c\i 4± • • co ••• 12.0 — cv .0 •
co O) 0 11.0 —
10.0 2.0
log (a /a ) K+ H+
Figure 24. Log[Ca 21- ]/[e] 2 versus log [e]/[e]. 90
13.0 -
12.0 -
11.0
10.0 -
9.0 2.0 310 4.0 5.b 6.10 log (a K.,/a H ,)
2+ Figure 25. Log [Mg ]/H+ ) 2 versus log [el/D-1+ J . 91
During the weathering of ultramafic, basaltic, and granitic rocks, the reaction of aluminosilicates with dissolved carbon dioxide is accompanied by a release of cations and silicic acid, as represented schematically by the following equation (Stumm and Morgan, 1981):
Cation Al silicate(s) + H 2 CO 3 + H 2 0 =
HCO 3 - + H4 SiO4 + Cation + Al silicate(s)
The silica concentration of groundwater in the Ranegras Plain basin averages 29 mg/l. This relatively high concentration suggests that silicate hydrolysis is an important controlling reaction.
If feldspar weathering is the dominant mineral weathering reac- tion controlling the groundwater chemistry, then the relative ratios of dissolved sodium, calcium, and potassium in the groundwater will be dependent on the feldspar composition, the ratio of plagioclase to orthoclase, and the ratio of kaolinite, montmorillonite, and illite formed by the reactions. The following reaction is the incongruent dissolution of andesine plagioclase to form kaolinite:
+ 4 Na0.5 Ca0.5A1 1.5 Si 2.5 0 3 + 6 H + 11 H 2 0 = + 2+ 2 Na + 2 Ca + 4 H4 8iO 4 + 3 Al 2 Si 2 0 5 (OH) 4
The alkalinity of the groundwater increases during this process of silicate hydrolysis, and, if it rises high enough, calcite may pre- cipitate. This process would account for the lower bicarbonate concen- trations found in the center of the Ranegras Plain basin. Groundwater in the majority of the basin is saturated with respect to calcite. 92
Minerals of the kaolinite group are the are the most common alteration products of the weathering of feldspars. Smectites and micas are possible products or intermediates. Kaolinite may further react to form calcium and sodium smectite (montmorillonite) as represented by the following two equations:
31/2 kaolinite + 4 H4 SiO4 + Na 3 Na-smectite + H-1- + 111/2 H 20
2+ + 7 kaolinite + 8 H 4 SiO4 + Ca = 3 Ca-smectite + 2 H + 23 H 2 0
Dissolution of Evaporites
Three lines of evidence indicate the dissolution of evaporites in the Ranegras Plains basin: (1) the elevated concentrations of sodi- um, calcium, sulfate, and chloride in the groundwater, (2) the presence of gypsum in well cuttings as previously discussed in Chapter 2, and (3) the large differences of dissolved mineral content in nearby wells at some locations of the basin.
Large changes in the mineral content of groundwater over short distances are frequently due to the dissolution of evaporites. The chemical content of groundwater from Wells No. 13, 15, 34, and 35 is characterized by elevated calcium (110-340 mg/1), sodium (200-950 mg/1), chloride (138-800 mg/1), and sulfate (660-1900 mg/1) concentrations.
The presence of gypsum or other evaporites in the basin sediments is the suspected source of the dissolved minerals. The large sodium concentra- tions are due in part to ion exchange, as explained in the following section. 93
Table 5 compares the groundwater quality of Wells No. 15 and 16, which are within a few hundred feet of each other, but yield groundwater of markedly different composition. Groundwater from Wells No. 15 and 16 contains approximately the same concentration of sodium, potassium, magnesium, chloride, and bicarbonate, but very different values for calcium and sulfate. The differences in calcium and sulfate concentra- tions between the two well samples are 11.6 and 12.7 meq/l, respective- ly. This relatively close mass balance strongly supports the dissolu- tion of gypsum as the source of the elevated calcium and sulfate in the groundwater of Well No. 15. The dissolution of gypsum is reflected in the higher gypsum saturation index for groundwater from Well No. 15 compared to groundwater from Well No. 16 (Table 5).
The perforated interval for Wells No. 15 and 16 are 0-1005 feet and 300-1100 feet, respectively. The much lower TDS of groundwater from
Well No. 16 suggests that groundwater of lower TDS may be present below the gypsiferous interval observed from 700 to 920 feet depth in the southern part of the basin.
Cation Exchange
Cation exchange of sodium for calcium appears to be a dominant controlling reaction of the hydrogeochemistry of the Ranegras Plain basin. The normality of sulfate in the groundwater is generally much less than that of calcium; therefore, the high sulfate concentrations cannot be explained by the dissolution of gypsum alone.
Calcium in solution may exchange for sodium adsorbed on clays by cation exchange. As predicted by the double layer theory, the affinity 94
Table 5. Comparison of chemical analyses of groundwater samples from Wells No. 15 and 16.
Well No. 15 Well No. 16 Difference
(mg/1) (meq/l) (mg/1) (meq/l) (meq/l)
Calcium 260 12.97 27 1.35 11.62
Sodium 200 8.70 170 7.40 1.30
Potassium 4.4 0.11 3.7 0.10 0.01
Magnesium 4.9 0.40 3.2 0.25 0.15
Sulfate 780 16.24 170 3.54 12.70
Chloride 140 3.95 120 3.39 0.56
Bicarbonate 88 1.44 58 0.95 0.49
Fluoride 3.6 0.19 5.3 0.28 0.09
TDS 1530 601 pH 7.7 8.0
Well Depth 1005 1242 (feet) Perforated 0-1005 300-1100 Interval (feet)
Calcite S. I 0.192 -0.537
Gypsum S. I. -0.235 -1.491 95 of clays for bivalent ions such as Ca2+ is larger than that for mono- valent ions such as Na+ , and this selectivity for ions of higher valency decreases with increasing ionic strength of the solution (Stumm and
Morgan, 1980). The removal of calcium by ion exchange may allow the pH to rise above pH 8, because buffering by calcium carbonate becomes rela- tively ineffective (Hem, 1970).
Robertson (1986) reported that the majority of alluvial basins in southern Arizona contain clay almost entirely of montmorillonite composition. Montmorillonite has a higher exchange capacity and greater selectivity for divalent ions than kaolinite or illite (Wiklander,
1964). The adsorbed cations on the clays in the Ranegras Plain basin are likely primarily sodium, since calcium was removed from the playa brines during clay deposition by gypsum precipitation.
A comparison of the groundwater from Wells No. 35 and 36 demon- strates cation exchange in the groundwaters of the Ranegras Plain.
Although Wells No. 35 and 36 are within approximately 1000 feet of each other, water from Well No. 35 contains concentrations of calcium, sodi- um, magnesium, chloride, and sulfate which are approximately 3 to 5 times greater than water from Well No. 36 (Table 6). The concentrations of potassium, bicarbonate, and fluoride are similar in groundwater from both wells. The increase in calcium is not equimolar with the increase of sulfate; therefore, the increase in these two ions may not be attrib- uted only to the dissolution of gypsum. The ratio of the meq/1 of the major ions in Well No. 35 to that of Well No. 36 is approximately the same for calcium and sulfate, and for sodium and chloride. This 96
Table 6. Comparison of chemical analyses of groundwater samples from Wells No. 35 and 36.
(a) Ion Well No. 35 Well No. 36 Difference Ratio
(mg/1) (meq/l) (mg/1) (meq/1) (meq/l)
Calcium 340 16.97 76 3.79 13.18 4.478
Sodium 950 41.33 340 14.79 26.54 2.794
Magnesium 80 6.58 15 1.23 5.35 5.350
Potassium 12 0.31 8.7 0.22 0.09 1.409
Sulfate 1900 39.56 430 8.95 30.61 4.420
Chloride 800 22.57 280 7.90 14.67 2.857
Bicarbonate 121 1.99 122 2.00 0.01 0.995
Fluoride 4.5 0.24 4.8 0.25 0.01 0.960
TDS 4260 1280 pH 7.7 7.6
Well Depth 1100 1000 (feet)
Perforated 190-1000 500-1000 Interval (feet)
Calcite S. I. 0.040 0.001
Gypsum S. I. 0.070 -0.913
(a) meq/1 Well No. 35 per meq/1 Well No. 36 97 suggests that although calcium and sulfate are introduced into the groundwater by the dissolution of gypsum, the concentration of calcium in solution is being reduced through the ion exchange of sodium for calcium.
The hypothesis of cation exchange is tested with the following assumptions:
1. The increase in calcium, sodium, magnesium, sulfate, chloride,
and fluoride is due to the dissolution of gypsum (CaSO 4 -2H2 0),
halite (NaCl), and epsomite (MgSO 4 -7H20). Groundwater from Well
No. 35 is saturated with respect to gypsum (Table 6). Epsomite
was most observed in well cuttings, but was included in the
calculations to balance the magnesium and sulfate.
2. The contribution from the weathering of silicate minerals is
small relative to the contribution from the dissolution of evap-
orites. This is reasonable based on the concentrations of ions
measured in spring samples due to the weathering of granite
(Carrels and Mackenzie, 1967).
3. The removal of calcium by calcite precipitation is not a signi-
ficant reaction at this location. This assumption is supported
by the close agreement of the bicarbonate values of the two
wells. Both wells are saturated with respect to calcite
(Table 4). 98
Assuming that all chloride originates from the dissolution of
halite, the sodium surplus is 11.87 meq/1.
sodium = 26.54 meq/1
- chloride — 14.67 meq/1
sodium surplus — 11.87 meq/1
Assuming that all sulfate originates from the dissolution of gypsum and
epsomite, the calcium deficiency of 12.08 meq/1.
sulfate — 30.61 meq/1
- magnesium 5.35 meq/1
- calcium — 13.18 meq/1
calcium deficiency — 12.01 meq/1
The close correlation of the sodium surplus and the calcium deficiency between these two nearby wells supports the concept of cation exchange
as a dominant reaction controlling the groundwater chemistry at this
location. CHAPTER 6
STRONTIUM HYDROCHEMISTRY OF THE RANEGRAS PLAIN BASIN
This chapter discusses the occurrence and distribution of stron-
tium in the groundwater of the Ranegras Plain basin and the correlation
of strontium with other dissolved constituents in groundwater. Four
mechanisms potentially controlling the concentration of strontium in
groundwater are evaluated: (1) dissolution of celestite and stron-
tianite; (2) release of strontium during the weathering of silicate minerals; (3) the solid solution of strontium in calcite, aragonite, and
gypsum; and (4) cation exchange.
Summary
Strontium concentrations in the groundwater of the Ranegras
Plain basin range from 0.060 mg/1 to 4.1 mg/l. The concentrations are greatest in the northern part of the basin and in the groundwater from two wells associated with evaporites and volcanics in the central and western part of the basin. Strontium correlates positively with cal- cium, sulfate, and total dissolved solids.
The primary source of strontium in groundwater appears to be from gypsum dissolution. Secondary sources are the weathering of sili- cate minerals and the release of adsorbed strontium on clays.
99 100
Strontium concentrations are controlled by the pH of the ground- water. The greatest concentrations occur at pH values less than 7.7.
The dependence of strontium and calcium concentrations on pH support the hypothesis of solid solution of strontium in calcite and is consistent with cation exchange of strontium on aquifer sediments.
Calculated Sr/Ca molar ratios for gypsum and aragonite using solid solution theory and groundwater analyses from the Ranegras Plain agree with published values within a factor of 6. The likely mechanisms limiting the concentration of strontium in groundwater are the solid solution of strontium in calcite and aragonite with which the ground- water is approximately saturated, and adsorption and desorption of strontium from clays and sesquioxides.
Occurrence and Distribution of Strontium in Groundwater
The concentration of strontium in groundwater in the Ranegras
Plain Basin ranges from 0.060 mg/1 to 4.4 mg/1 (Table 1, Figure 26).
The concentration generally increases from south to north in the basin.
The lowest concentrations occur in the interior of the southern half of the basin and are generally less than 0.20 mg/l. Wells at the perimeter of the southern half of the basin (Wells No. 3 and 5) contain signifi- cantly higher strontium concentrations than those of the interior wells in the southern half of the basin. Groundwater from wells in the north- ern half of the basin contains from 0.40 mg/1 to 4.1 mg/1 strontium.
The highest concentrations (greater than 2.0 mg/1) occur in the area to the south and west of the Bouse Hills and in two isolated wells in the 101
0 5SCALE IN MILES
Strontium 0.20 Concentration (mg/0
Figure 26. Strontium concentrations in groundwater. 102 basin center (Well No. 15) and at the western perimeter of the basin
(Well No. 21).
A histogram of the strontium concentration in groundwater sam- ples from the Ranegras Plain is shown in Figure 27. The most commonly occurring concentrations range from 0 to 0.75 mg/1 strontium. The num- ber of samples in each successively higher concentration category decreases exponentially up to a value of 3 mg/l. A separate cluster of strontium concentrations occurs in the range of 3.75 to 4.5 mg/l.
The cumulative frequency distribution of strontium activities in the well samples from the Ranegras Plain basin approximates a log normal distribution (Figure 28). The median activity is 3.4 x 10 -6 .
Correlation of Strontium with Other Dissolved Constituents in Groundwater
Statistical correlations of the strontium concentration with dissolved constituents and chemical and physical parameters of ground- water samples from wells in the Ranegras Plain basin were completed using the SPSS computer program (Nie et al. 1975). The correlation coefficients are listed in Table 7, and scatttergrams are presented in
Figures B-1 through B-23 (Appendix B) and Figure 29.
Strontium positively correlates with calcium, magnesium, sul- fate, residue, total hardness, and noncarbonate hardness. Residue is the total concentration of dissolved material in water determined from the weight of the dry residue remaining after evaporation of the water sample. The strongest positive correlations are with calcium and sul- fate. The high positive correlation with noncarbonate hardness and 103
15
1 0
0 0 5 1 0 1 5 20 25 30 35 40 45
STRONTIUM CONCENTRATION IN WELL SAMPLES (mg/I)
Figure 27. Histogram of strontium concentrations in groundwater samples from wells in the Ranegras Plain basin. 104
•
. •
• • •
. •
• . • •
• •
•
ps 1 0 1 1 1 t 1 1 t i 0 0 0 0 0 0 0 0 0 0 0 0 0 ". 0 CO CO CO P. 40 10 et CO OA 1- 1- ( uo!4nqp4sm 44ificieqord itnuioN ) (IN301:13d) A3N311031:1A anwrinvino 105
Table 7. Correlation coefficients of strontium with other dissolved constituents and physical and chemical parameters.
Correlation Coefficient 2 (R)
MAJOR IONS
Calcium 0.743 0.552 Magnesium 0.473 0.224 Potassium 0.321 0.103 Sodium 0.073 0.005
Sulfate 0.527 0.278 Chloride 0.133 0.018 Bicarbonate 0.184 0.034 Carbonate -0.273 0.075 Fluoride -0.399 0.159 Silica 0.303 0.092
TRACE ELEMENTS
Arsenic -0.429 0.148 Barium 0.382 0.146 Boron -0.100 0.010 Lead -0.081 0.006 Lithium 0.530 0.282 Selenium 0.171 0.029 Vanadium -0.535 0.286
PHYSICAL AND CHEMICAL PARAMETERS pH -0.561 0.315 Residue 0.473 0.224 Well Depth 0.200 0.040 Temperature -0.105 0.011 Noncarbonate Hardness 0.654 0.427 Total Hardness 0.785 0.617 106 total hardness results from the correlation of strontium with both cal- cium and magnesium. The positive correlation of strontium with calcium and sulfate suggests that the dissolution of gypsum or calcite contain- ing strontium as a trace constituent may be responsible for the occur- rence of strontium in groundwater.
pH has a primary control on the strontium concentrations in groundwater. The pH and the maximum strontium concentration at each pH value are negatively correlated as shown by Figure 29. All four well water samples with strontium concentrations equal to or greater than 4 mg/1 have a pH of 7.7 or below. All well samples with pH 8.2 or greater have strontium concentrations equal to or less than 0.22 mg/l.
Strontium concentrations correlate negatively with pH, fluoride, arsenic, and vanadium. The negative correlation of strontium with fluoride (Figure B-9) is likely due to the saturation of groundwater with respect to fluorite. Fluorite saturation results in a negative correlation between calcium and fluoride, and strontium is positively correlated with calcium.
The negative correlation of strontium with arsenic and vanadium may be a result of a mutual pH-dependence of these two ions or a common ion effect.
Mechanisms Controlling the Strontium Concentrations in Groundwater
Four geochemical mechanisms that may potentially control the concentration of strontium in groundwater were considered as multiple 107
5.0
• • • •
•
• • • • • • • • • • • • • • • • • 8 • • 8 4 0.0 . . _ . 7.0 7.5 I 8.0 8.5 pH (units)
Figure 29. Strontium concentrations in groundwater versus pH. 108 working hypotheses in this thesis and are listed below:
(1) Dissolution of celestite and strontianite
(2) Release of strontium during the weathering of silicate minerals
(3) Solid solution of strontium in calcite, aragonite, and gypsum
(4) Cation exchange
These potential mechanisms are discussed separately in the following sections.
Dissolution of Celestite and Strontianite
No direct evidence exists for the presence of celestite (SrSO 4 ) or strontianite (SrCO 3 ) in exposed rocks or in drill cuttings from the
Ranegras Plain basin; however, these two minerals occur in significant concentrations at locations in western Arizona and southern California, as previously described in Chapter 4. These strontianite and celestite deposits occur in association with evaporite deposits, volcanic tuffs or lava flows, and hydrothermal mineralization. All three rock types are present at the Ranegras Plain basin. Gypsum deposits are present in the
Plomosa Mountains, Granite Mountains, and the basin sediments below a depth of 700 feet. Tertiary basalt flows and tuffs, and Cretaceous andesites are common in the mountains surrounding the basin. Past hydrothermal activity is shown by the presence of base metal deposits in the Plomosa Mountains and Granite Wash Mountains.
Saturation of groundwater with respect to strontianite and celestite does not, however, appear to be a controlling factor of the strontium concentrations in groundwater of the Ranegras Plain basin. 109
Strontianite and celestite may contribute to elevated strontium concen- trations, but both minerals are undersaturated in the groundwater an average of one order of magnitude or greater. The saturation index of strontianite ranges from -1.984 to -0.564 and averages -1.357 for the basin. The saturation index for celestite ranges from -3.077 to -0.626 and averages -1.938 (Table 4).
Strontium concentrations in groundwater as a function of the saturation index of strontianite and celestite are shown on Figures 30 and 31, respectively. As expected, the strontianite and celestite saturation indices becomes less negative as the strontium concentration increases. The well samples with the highest strontianite saturation indices (i.e. greater than -1.0) are from Wells No. 21, 28, 31, 36, and
40. These wells are in the northern part of the basin, with the excep- tion of Well No. 21, located in the western margin of the basin in a groundwater recharge area.
The well samples with the highest celestite saturation indices
(i.e. greater than -1.0) are from Wells No. 15, 21, and 36. Well No.
15, a deep well in the basin center, produces groundwater containing 780 mg/1 sulfate. Groundwater from Well No. 21 contains only 250 mg/1 sul- fate. Well No. 36 is in the northern part of the basin where the high- est sulfate concentrations occur; groundwater from Well No. 36 contains
430 mg/1 sulfate. Well No. 40 is adjacent to Bouse Wash in a recharge area, and, therefore, appears anomalously undersaturated with respect to celestite due to the relatively low sulfate concentration. 110
5.0
• • • 4.0
3.0 •
• • 2.0 • • • • P • 1.0 - I • • .41 • • • • • • 0.0 • • • • . . . n . -2.00 1.5 LO0 -050 0.00 Strontianite Saturation Index
Figure 30. Strontium concentration in groundwater versus strontianite saturation index.
5.0
4.0 0")
3.0 o o 2.0 =
I .
0 nft, L. LO ; Ul • • ao •• • • -350 -300 -250 -200 -150 -100 -050 0.00 Celestite Saturation Index
Figure 31. Strontium concentration in groundwater versus celestite saturation index. 111
The dissolution of celestite is consistent with the observed correlation of strontium with sulfate. Because celestite commonly occurs with gypsum, the dissolution of celestite would also support the correlation of strontium with calcium. Localized strontianite or celes- tite saturation may occur in specific depth intervals at some locations in the basin, but be masked by dilution with water from underlying or overlying strata during the pumping of the well.
Release of Strontium During the Weathering of Silicate Minerals
Strontium exists as a trace element in calcium-containing sili- cate minerals and may be released into groundwater during the weathering of these minerals. Based on the concentration of strontium in rock types reported in the literature, Tertiary basalts and andesites are the most likely sources of strontium due to silicate mineral weathering.
Turekian and Kulp (1956) reported an average strontium concentration of
337 ppm in granite (western United States) and 943 ppm strontium in
Tertiary basalts and andesitic flows. Krauskopf (1967) reported that of the igneous rocks, strontium is highest in andesine andesite (2500 ppm) and oligoclase andesite (3500 ppm).
Andesite is found primarily in the Bouse Hills, Plomosa Moun- tains, New Bear Hills, and New Water Mountains on the northern and west- ern perimeter of the Ranegras Plain groundwater basin (Figure 3). Mid- to Late Tertiary basalts are found in the vicinity of Pyramid Peak, at the southern tip of the New Bear Hills, in the southern New Water Moun- tains, and in the northern Little Horn Mountains on the east-central, 112
west-central, and southern perimeter of the groundwater basin. Both
rock types are potential sources of strontium. The highest strontium
concentrations in groundwater occur in the northern part of the basin
where large surface exposures of andesite are present.
The association of strontium deposits with Tertiary volcanic
tuffs and flows in southern California and western Arizona was discussed
in Chapter 4. Volcanic tuffs and olivine basalts have been weathered to
bentonite clay in the alluvium below the flanks of the Bouse Hills
directly east of the town of Bouse. Groundwater from wells in this
vicinity (Wells No. 41 and 42) contain 2.2 mg/1 and 1.7 mg/1 strontium,
respectively.
The weathering of silicate minerals releases calcium and stron-
tium into groundwater in the approximate ratio in which they appear in
the rock. If neither element adsorbs or precipitates selectively, then
the strontium/calcium ratio of the groundwater should be approximately
the same as the rock.
The weathering of feldspars is consistent with the positive
correlation of dissolved calcium and strontium. The weathering reaction
consumes acid (dissolved carbon dioxide), and thus results in a pH
increase. If no other process were controlling the strontium concentra-
tion, the highest concentrations would be expected at the higher pH values. This is not the case, because two other processes act to reduce
• the strontium concentration at more basic pH values: cation adsorption
on clays and coprecipitation of strontium with calcite. Most of the
groundwater in the basin is at saturation with respect to calcite. 113
Strontium released from the weathering of basalts, tuffs, and
andesites in the Ranegras Plain may have been incorporated as a trace
component in gypsum and anhydrite or as minor quantities of celestite
during the precipitation of these evaporites in the basin fill.
Solid Solution of Strontium in Calcite, Aragonite, and Gypsum
Strontium occurs as a trace element in calcite, aragonite, and
gypsum by substituting for calcium in the crystal structure of these two
minerals by a process known as solid solution. Therefore, the dissolu-
tion or precipitation of either mineral is a potential mechanism for
controlling the strontium concentration in groundwater. The dissolution
of any of these three minerals would produce the positive correlation of
strontium and calcium shown in Figure B-1.
Solid Solution of Strontium in Calcite
This section discusses sources of calcite with the Ranegras
Plain basin aquifer and the degree and extent of saturation of ground- water with respect to calcite. The concentrations of calcium in groundwater are then compared to that predicted by the system CaCO 3 -H2 0-
CO2 plus acid or base.
Calcite Sources. Two sources of calcite exist in the Ranegras
Plain groundwater basin: (1) eroded limestone detritus from the Meso- zoic sedimentary sequence in the Granite Wash and Plomosa Mountains, and
(2) the calcite cement present in the upper basin fill and lower basin fill. Chapter 7 discusses the analysis of limestone from the 114
surrounding mountains and the acid-extractable fraction of well cuttings
from the Ranegras Plain basin.
Detailed lithologic logs for Ranegras Plain wells are available
only for wells No. 7 [B(3-15)2dab], B(3-14)11ddc, B(7-17)15dcd, and
B(7-17)23cdc. The well logs for Well No. 7 and B(7-17)15 dcd are in
Appendix A. Limestone fragments were reported only for Well No. 7.
These fragments constitute less than a few percent of the total sediment,
and were found at depths of 140 to 480 feet and 700 to 840 feet.
The logs for Wells No. 7 and B(3-14)11ddc reported the presence
of calcite coatings on sediment grains as tested by the evolution of
carbon dioxide with hydrochloric acid. Drill cuttings from Well
No. 7 exhibited a moderate reaction with (HC1)from a depth of 160 to 320
feet, a strong reaction from 340 to 880 feet, and a moderate reaction
from 800 to 960 feet. Cuttings from Well B(3-14)11ddc exhibited a mod-
erate reaction from 10 to 290 feet, and a weak reaction from 290 to 650
feet.
Wells B(7-17)15dcd and B(7-17)23cdc, are in the northwest part
of the basin near the town of Bouse. Drill cuttings from these wells
contain visible calcite coatings at depths from 0 to 10 and 55 to 90
feet, and from 0 to 30 feet, respectively.
Calcite Saturation. The calcite saturation index for ground- water samples from the Ranegras Plain is shown in Figure 32. The majority of wells in the basin contain groundwater slightly undersatu-
rated with respect to calcite. The saturation index for the majority of
groundwater samples from the basin interior is between -0.25 and -0.10. 115
• -0.129 • -0.215 • -0.178° *0.270 0.071 II0 . 019) • -0.304 •*0.123 0.159° •4,0.040 0.001 • • -0.079 • -0.171 -0.481. -0.139 -0.169
-0.419 • -0.223 600 • -0.483 • 1 -0.082 • -O.1570.255 <4,41 -0.484 ;0.701 ••• -0.539 -0.256 • -0.435 ..17.03 .811 2 • 0.133% -0.149
• -0.513 -0.096
• -0.027
C:2. 0.0.228
0!niin4 Szb SCALE IN MILES
Calcite 1.025 Saturation Index
Figure 32. Saturation of groundwater with respect to calcite. 116
Wells in the southern part of the basin contain groundwater closer to
saturation (-0.1 > S.I. > 0.0). The most highly undersaturated well
samples occur on the western border of the northern half of the basin,
possibly due to a greater amount of recharge in that area.
The only wells yielding groundwater above saturation are in the
southwest corner of the basin (Wells No. 2 and 3), in the north central
part of the basin (Wells No. 31, 34, 35, 36, and 50), in the northwest
corner of the basin (Well No. 40), and on the western perimeter of the
basin (Well No. 21). Wells No. 3, 21, and 40 are in recharge zones;
the oversaturation of groundwater samples from these wells with respect
to calcite may be due to the dissolution of precipitated calcite cement
in the aquifer sediment at the near surface.
Groundwater samples from the other two wells in recharge zones,
Wells No. 5 and 9, have calcite saturation indices of -0.029 and -0.484,
respectively. The significant undersaturation of groundwater from Well
No. 9 suggests that the rate at which calcite saturation can be reached
at Well No. 9 is limited by the weathering rate of aluminosilicate min-
erals. The basin sediment at the location of that well is primarily
coarse granitic grus.
These calcite saturation values suggest that the dissolution of
calcite in the aquifer matrix is a reasonable source for both dissolved
calcium and strontium. The oversaturation of calcite in groundwater
from those wells in the north central part of the basin may be due to borehole mixing of deep groundwater containing high concentrations of calcium, sulfate, and chloride. 117
Strontium concentration versus calcite saturation index for well samples in the Ranegras Plain basin is shown in Figure 33. This graph demonstrates that samples from four of the five wells containing the highest strontium concentrations (Wells No. 15, 21, 31, and 40) are oversaturated with respect to calcite.
Figure 34 demonstrates that groundwater attains calcite satura- tion prior to reaching strontianite saturation. Samples from wells oversaturated with respect to calcite have the highest strontianite saturation indices (-1.0 < S.I. < -0.5); however, these samples are still significantly undersaturated with respect to strontianite.
Figure 35 indicates no direct relationship between pH and the calcite saturation index. Individual groundwater samples occur at or below calcite saturation over a range of pH 7.1 to pH 8.4. With the exception of the samples from Well No. 2, all samples oversaturated with respect to calcite occur in the range pH 7.4 to pH 7.8.
Calcium Concentrations Calculated from the Model CaCO 3 -H20-0O2
Plus Acid or Base. The calculation of aqueous calcium concentrations from calcite dissolution is represented by the model CaCO3 -H2 0 -0O2 plus acid or base, when the system is in equilibrium with CO 2 gas (Stumm and
Morgan, 1981; Carrels and Christ, 1965).
Assuming that: (1) equilibrium with calcite provides all calcium in solution, (2) calcium does not participate in any other reactions, and (3) other major cations and anions are not present in solution, the solution must fulfill the condition of electroneutrality:
C(B) + 2[0a24- ] + [e] [HCO3-] + 2[CO 3 2 1 + [OH - ] + C(A) (6.1) 118
5.0
cn 4.0
6 3.0 o
2.0
o 1.0 (n
0.0 -1 00 -050 0.00 0.50 Calcite Saturation Index
Figure 33. Strontium concentration in groundwater versus calcite saturation index.
-0.5 • (ll • , • • _ • • • • • • • .
• • • -1.5 • • • • • • • • • .
• -0.8 -d.6 -0.2 0.0 0.2 0.4 Calcite Saturation Index
Figure 34. Strontianite saturation index versus calcite saturation index. 119
0.4
• 0.2 a • • • • s • • • • • • •
• • e • • • 1 • • • • • • 8 • • • -0.4 • • • s • • o • o o -0.6
•
-0.8 . . 7.0 7.5 ' 8.0 8.5 pH (units)
Figure 35. Calcite saturation index versus pH of groundwater. 120 where C(A) and C(B) represent added acid and base, respectively. The system is controlled by the solubility of calcite, and the equilibrium equations relating the partial pressure of CO2 gas (pCO 2 ), [H2 CO 3 ],
[HCO 3 - ], [CO 3 2 1 , and [e]. All concentrations are expressed as activi- ties, and equilibrium constants are given at 25°C.
2+ 2- CaCO 3 (s) - Ca + CO 3 Kcal - [Ca2+ ] [CO 3 2- ] (6.2) = 10 -8.42
CO 2 (g) + H 2 0 - H 2 CO 3 Kh - [HCO 3 ]/pCO 2 (6.3)
- 10 -147 + H2 CO 3 = H + HCO 3 - Ki [H+ ][HCO 3 - ]/[H2 CO 3 ] (6.4) - 10 -6 ' 35 2- + 2- + HCO3 = C O 3 + H 1(2 - [CO 3 ][H 1/[HCO 3 - ] (6.5) = 10 -10 ' 33
All carbonate species can be expressed in terms of [e] and pCO2 .
[H2 CO 3 ] - Kh (pCO2 )
[HCO 3 - ] K1 [H2 CO 3 ]/[e] = KiKh (pCO2 )/[11-1- ]
[CO 3 2- ] K2 [HCO 3 - ]/[e] = K2K1Kh (pCO 2 )/[11-1 ] 2
The concentration of calcium can be expressed in terms of the calcite solubility product.
{Ca 2-1 } = K=cal/ Kcal[144-12[C° 3 2-] /K2K1Kh(pCO2) (6.9)
log [Ca24- ] - log [Kcal/K2K1Kh (pCO2 )] - 2 pH (6.10) 121 2+ Thus a plot of log [Ca ] versus pH at a constant pCO 2 should have a slope of -2 for this system.
Log activity calcium is plotted versus pH for groundwater samples in the Ranegras Plain in Figure 36. The data points appear to generally have a slope of -2, as predicted by Equation [1]. Theoretical calcite saturation lines are shown for log(pCO2 ) values between -2.20 and -3.20 (after Stumm and Morgan, 1981). Log(pCO 2 ) values for ground- water samples in the Ranegras Plain basin range from -3.456 (Well
No. 20) to -1.92 (Well No. 5) and average -2.599.
The measured calcium activities for groundwater samples with calcite saturation indices between -0.1 and +0.1 were compared to cal- cium activities predicted by Equation (1) at the sample pH and pCO2 . The calcium activities for those well samples with the highest calcium con- centrations are greater than that predicted by the calcite dissolution model (Wells No. 15, 35, 21, 40, and 41). These well samples have rela- tively high sulfate concentrations; therefore, the additional calcium may be due to gypsum dissolution. Those samples with relatively low calcium concentrations (Wells No. 2 and 8) have lower calcium activities than predicted by calcite dissolution. This discrepancy may be due to cation exchange of calcium for sodium or a larger percentage of calcium silicate hydrolysis in the southern part of the basin where these wells are located.
The groundwater samples from the Ranegras Plain contain signifi- cant concentrations of other major cations and ions other than calcium and the dissolved inorganic carbon species. These major ions are
122
-2.5 , \ \ \ \ \ \ \ \ • \ , \ \ \ \ \ , \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ N
\ • \ \ \ \ •\ \ \ \ \ \ \• \ \ \,. N .\ \
\ \ \ •\ \ \ ,0 \ \ I\ *\ • \- G \ \ :\ \c° \ \ \ \ . A `k,2 cs \ •\ \ \ \Gc, ‘.3 V-.) \ \ \ • \ \ (:),1",,t, \ • 0\ \ \/0_.0 \‘?0 \ \ \ \ \ \G • \ ` \
• N \ \ \ \ \PG6 \ \ \ \ \ \ \ 1$.} \d' • \ \ \ 6 \ \ \ ç'G • \ : 0-) —4.0 \ ,-,1 .) \ \ N o \ 6 t; \ \ __J ‘t \ \s \ N çl$Ço N N .f \ \ \ —4.5 7.0 7.5 8.0 8.5 pH (units)
(a) Theoretical line of calcite solubility at listed log (pCO2), open system
Figure 36. Log activity calcium versus pH. 123 predominantly sodium, chloride, and sulfate. These ions alter the carbonate equilibria, thus permitting more or less calcium to be present in groundwater in equilibrium with calcite. The general charge balance equation for this case (ignoring minor species) follows.
[Nat ] + [K-1- ] + 2 [Mg 2+ ] + 2 [Ca 2-1- ] —
[HCO 3 - ] + 2 [CO 3 2- ] + [C1 - ] + 2[SO4 2 1 (6.11)
This can be rewritten as:
2+ M + 2 [Ca ] — [HCO 3 - ] + 2 [CO 3 2- ] (6.12) where M = [Nat ] + [e] + 2 [Mg2+ ] - [C1 - ] - 2 [SO4 2 ] (6.13)
If the value for M is positive, then as M increases, the equili- brium concentration of calcium due to calcite saturation will decrease
(Dreyer, 1982). If the value of M is negative, then as M decreases, the equilibrium concentration of calcium due to calcite saturation will increase.
The values of M for well samples in the Ranegras Plain are listed in Table 1. With the exception of Well No. 5, well samples near calcite saturation in the southern part of the basin (Wells No. 1,
2, 7, and 8) have positive values of M. The calcite-saturated well samples in the central and northern part of the basin have negative M values (Wells No. 14, 15, 21, 22, 28, 29, 35, 36, 38, and 42) due to high chloride and sulfate concentrations. Samples from Wells No. 15 and
35 have the most negative M values, and the highest sulfate concentra- tions in the basin. Molalities of chloride and sulfate greatly 124 exceeding that of sodium, potassium, and magnesium in groundwater sampl- es from Wells No. 15 and 35 greatly increases the concentration of calcium permitted by calcite saturation.
Solid Solution of Strontium in Gypsum
The positive correlation of strontium with sulfate (Figure B-5) and evaluation of gypsum saturation indices suggest that strontium occurs in solid solution with gypsum or that localized deposits of celestite may be interbedded with gypsum.
Gypsum is present in the well cuttings of Well B(3-15)2dab between the 700 and 920 foot depth (Appendix A). One to five percent gypsum occurred from a depth of 700 to 780 feet, with the largest con- centration at 780 feet depth.
Figure 37 shows the strontium concentration versus the gypsum saturation index for groundwater samples from the Ranegras Plain basin.
With the exception of Well No. 40, well samples with the highest stron- tium concentrations have the highest gypsum saturation indices (between
-1.00 and -0.235); the gypsum saturation index for the remaining well samples ranges from approximately -2.8 to -1.1. Water from Well No. 40 is highly undersaturated with respect to gypsum (S.I. — -2.547), indi- cating a strontium source other than gypsum. Groundwater from Well
No. 35 is saturated with respect to gypsum (S.I. — 0.070), but a stron- tium analysis is not available for that well sample.
Many well samples in the north-central part of the basin contain greater than 250 mg/1 sulfate, yet these groundwater samples are 125 5.0
• • • on 4.0 -
3.0
•
• n 2.0 • • • • • • e 1.0 • • • • e• • • r • • • • • • • 0.0 -3.00 -2.00 -1.00 0.00 Gypsum Saturation Index
Figure 37. Strontium concentration in groundwater versus gypsum saturation index.
1.0
0.5 • SR Concentration 2:1 mg/I NS — No SR Analysis
NS 00
-0.5 •NS
NS. ' • At - 1 o • • A + • ..• • • • • -1.5 • • • . • • • _ • • . . : • • •
-3.0 1 I -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 Calcite Saturation Index
Figure 38. Gypsum saturation index versus calcite saturation index. 126 undersaturated with respect to gypsum by a factor of 10 or more. Bore- hole mixing may dilute gypsum saturated waters that occur at specific depth intervals, so that samples from the pumped well are undersaturat- ed. This concept is consistent with the fact that gypsum was found in only 80 feet of the 780 feet of sediments below the water table inter- sected by Well No. 7.
The relationship of the saturation indices of gypsum and calcite for well samples in the Ranegras Plain is shown on Figure 38. Well samples containing 1 mg/1 strontium or more are identified. These high strontium well samples are either oversaturated with respect to calcite or are within 11/2 orders of saturation with respect to gypsum. Elevated calcium concentrations will increase the saturation with respect to both gypsum and calcite. Since gypsum is more soluble than calcite, the mixing of calcium sulfate rich waters may result in water oversaturated with respect to calcite.
Solid Solution Calculations
Strontium may exist in solid solution with calcite, aragonite, gypsum, and anhydrite. Strontium is the primary minor constituent sub- stituting for calcium in these minerals. The strontium content of these minerals can be related to the Sr/Ca molar ratio of the solution in equilibrium with the mineral at the time of its deposition by the following equation:
(Sr/Ca) mineral — D (Sr/Ca) solution (6.14) where D represents the partition coefficient (McIntire, 1963; Garrels 127 and Christ, 1965; Dreyer, 1982), also known as the distribution constant
(Stumm and Morgan, 1982). The partition coefficient is an experimental- ly determined value. The Sr/Ca ratio of the mineral is the mole fraction of strontium divided by the mole fraction of calcium. The
Sr/Ca ratio of the solution is the ratio of molalities of Sr and Ca.
This equation the predicts the Sr/Ca ratio of a mineral from the Sr/Ca ratio in groundwater in equilibrium with that mineral. Conversely the
Sr/Ca ratio of the groundwater can be predicted from the Sr/Ca ratio in the groundwater. Equation 7 demonstrates that when the partition coef- ficient is greater than 1, the concentration of strontium will be enriched in the solution relative to the mineral phase. When the parti- tion coefficient is less than 1, the Sr/Ca ratio will be less in the solution than in the mineral phase.
Published Values of Partition Coefficients. Numerous authors have determined partition coefficients for calcite, aragonite, and gyp- sum. The partition coefficient for strontium in gypsum at 25°C was reported to be 0.30-0.41 by Purkayastha and Chatterjee (1966), 0.41-0.64 by Usdowski (1973), and 0.21-0.33 by Yamamoto and Uneki (1978). Ichi- kuni and Musha (1978) reported a partition coefficient of 0.21 at tem- peratures between 20 and 60°C; the partition coefficient was independent of the Sr/Ca ratio up to a Sr/Ca ratio (wt/wt) of 7.9 x 10 -3 . Butler
(1973) derived the partition coefficient of strontium in gypsum from geochemical data and reported a value of 0.19 at 28 ° C.
Kushnir (1980) studied the coprecipitation of Sr, Mg, Na, K, and
Cl into gypsum and reported that the partition coefficients generally 128 increase with brine higher concentrations, decrease with higher tempera- tures, and increase with higher crystal growth rates. Experimentally determined partition coefficients varied from 0.15 to 0.80 at 30°C and from 0.11 to 0.57 at 50°C.
Purkayastha and Chatterjee (1966) similarly reported that an increase in temperature tends to lower the partition coefficient for the coprecipitation of Sr in gypsum. Purser (1973) studied the distribution of strontium in gypsum and anhydrite formed in modern evaporitic envi- ronments. The average partition coefficient was 0.18 for gypsum.
Kinsman and Holland (1969) reported that the partition coeffi- cient of strontium in aragonite precipitated from sea water decreases linearly from 1.17 at 16°C to 0.88 at 80°C. Aqueous sulfate caused the partition coefficient to increase slightly due to complexing of sulfate with calcium and strontium. The experimentally determined partition coefficient at 20-25°C was 1.13. The partition coefficient for stron- tium in oolitic aragonite formed in the Great Salt Lake was reported to be 1.03 (Kinsman, 1969), 1.02-1.15 (Zeller and Wray, 1956), and 1.0
(Odum, 1957).
Kinsman and Holland (1969) reported that the partition coeffi- cient for strontium in calcite precipitated from sea water is 0.14.
Katz et al. (1972) reported a value of 0.05 for the partition coeffici- ent of strontium during the aragonite-to-calcite transformation based on a computer model of limestone diagenesis for the depletion of strontium in meteoric groundwater (Morrow and Mayers, 1978). The model was cali- brated by the amount of strontium lost by Barbados and Barbuda aragonite
129
during early diagenesis. Oxburgh (1959) determined the partition
coefficient for strontium in calcite of various compositions at 30°C.
Control of Strontium Concentrations by Equilibrium with Aragon-
ite and Strontianite. The following example demonstrates that if
groundwater is in equilibrium with strontianite and aragonite, the
strontium concentration in the groundwater will be much less than if the
strontium concentration is controlled by the solubility of strontianite
alone. The example will use data from the Great Salt Lake oolites and
brines (Kinsman, 1969).
The Sr/Ca ratio in the aragonite and brine will be described by
the following equation:
X SrCO3 [Sr2+] D (6.15) X [Ca24-] CaCO3
Solving for [Sr]:
X [Ca2-1- ] SrCO3 [Sr2+ ] (6.16) D X CaCO3 The calcium concentration in the groundwater may be expressed in terms
of the solubility product of aragonite, Ka .
2+ 2- [Ca ] [CO3 ] = Ka (6.17)
[Ca2-1- ] = Ka /[CO 3 2- ] (6.18)
Therefore the concentration of strontium in groundwater due to satura-
tion with aragonite, [Sr 2+ ] a , is given by the following equation: 130
Ka X SrCO 2+ 3 [Sr ] a — (6.19) D [CO3 2- ] X CaCO3
If the groundwater is saturated with respect to strontianite, then the aqueous strontium concentration due to saturation with stron- tianite may be expressed in terms of the solubility product, Ks .
[Sr2-1- ] 5 = K /[CO 3 2- ] (6.20)
Therefore the ratio of the strontium concentration due to saturation with Sr-aragonite to that due to saturation with strontianite is described by the following equation:
[Sr] a Ka X SrCO 3 = (6.21) [Sr] 5 D Ks X CaCO3
The values listed below will be substituted into Equation (6-21):
X SrCO 3 — 5.0 x 10 -3 (Kinsman, 1969), (6.22) X Great Salt Lake oolites CaCO 3
(Kinsman, 1969)
(Stumm and Morgan, 1981), 25°C
(Stumm and Morgan, 1981), 25°C 131
Therefore:
[ Sr] a 0.029 (6.23) [ Sr]
The concentration of strontium in the groundwater saturated with respect to aragonite is only 3 percent that of groundwater saturated with respect to strontianite. Saturation of the groundwater with respect to aragonite greatly reduces the dissolved strontium concentration that would occur from the dissolution of strontianite alone.
Calculation of Sr/Ca Ratios for Calcite . Aragonite, and Gypsum in the Ranegras Plain. Table 8 compares calculated Sr/Ca molar ratios in calcite, aragonite, and gypsum in the Ranegras Plain basin with pub- lished molar ratios for these minerals. The Sr/Ca molar ratios for the minerals were calculated with available groundwater analyses and equa- tion (6.14), assuming the solid solution of strontium with those minerals.
The Sr/Ca ratio for calcite and aragonite was calculated using the [Sr]/[Ca] ratio for groundwater from Well No. 40 and the average
[Sr]/[Ca] ratio for all wells in the basin. A sample from Well No. 40 was selected for analysis, because it is saturated with respect to cal- cite (S.I. = 0.178) and aragonite (S.I. = 0.063), is relatively under- saturated with respect to gypsum (S.I. — -2.547), and contains one of the highest strontium concentrations in the basin (4.0 mg/1). The aver- age groundwater in the basin is slightly undersaturated with respect to calcite (S.I. = -0.162) and aragonite (S.I. — -0.287) and undersatur- ated with respect to gypsum (S.I. = -1.487). 132
Table 8. Comparison of observed and calculated Sr/Ca molar ratios in calcite, aragonite, and gypsum based on the solid solution of strontium.
(a) Sr/Ca MOLAR RATIOS
Mineral Saturation Indices Groundwater Minerals
(b) (c) MINERAL SAMPLE D Calcite Aragonite Gypsum (observed) (calculated) (literature)
(d) (g) Calcite Basin Ave. 0.14 -0.162 -0.287 -1.487 9.2 1.3 NA
Well No. 40 0.14 0.178 0.063 -2.547 30 4.2 NA
(e) (d) Aragonite Basin Ave. 1.03 -0.162 -0.287 -1.487 9.2 9.5 5.0
Well No. 40 1.03 0.178 0.063 -2.547 30 3.1 5.0
(f) (h) Gypsum Well No. 15 0.18 0.192 0.075 -0.235 7.2 1.3 5.0
(a) Sr/Ca Molar Ratio = Moles strontium/1000 moles calcium
(b) D = partition coefficient
(c) (Sr)/(Ca] = D (ISr)/(Cal minerals groundwater
Kinsman (1969)
Purser (1973)
Kinsman and Holland (1969)
No data available for authigenic calcite
Ichikuni and Musha (1978) 133
The Sr/Ca ratio for gypsum was calculated using the [Sr]/[Ca]
ratio for groundwater from Well No. 15. A sample from Well No. 15 was
selected, because it is closer to gypsum saturation than any other well
sample in the basin with an available strontium analysis.
Relatively close agreement between Sr/Ca molar ratios for arago-
nite and gypsum reported in the literature and those values calculated
from the groundwater analyses suggests that the solid solution of stron-
tium in aragonite and gypsum is a likely mechanism for the control of
strontium in the groundwater of the Ranegras Plain basin. The Sr/Ca
ratio calculated for aragonite from the basin average is approximately
twice that measured for the Great Salt Lake aragonite. The calculated
Sr/Ca ratio for aragonite (Well No. 40) is approximately 6 times that of
the Great Salt Lake aragonite. The calculated Sr/Ca ratio for gypsum
(Well No. 15) is approximately 4 times that of gypsum formed in closed basins from the weathering of silicate rocks (Ichikuni and Musha, 1978).
No value for the Sr/Ca ratio in authigenic calcite was available for
comparison.
In chapter 7, the chemical analysis of drill cuttings from two wells in the basin will be used to test further the hypothesis of solid
solution as a potential mechanism controlling the strontium concentra-
tion in groundwater of the Ranegras Plain basin.
Cation Exchange
Cation exchange of calcium for sodium in the Ranegras Plain basin was demonstrated in Chapter 5 by the ratio of sodium to calcium in groundwater from interior basin wells and by the comparison of the 134
analyses of groundwater from nearby wells. This section discusses the
adsorption behavior of strontium onto minerals and attempts to quantify
the extent of strontium adsorption on the clays in the Ranegras Plain basin.
Strontium adsorbs on soil and aquifer sediments including clay minerals (e.g. kaolinite, vermiculite, and montmorillonite), aluminosil-
icate minerals (e.g. feldspar and biotite), hydrous metal oxide coatings
of iron, manganese, and aluminum (known collectively as sesquioxides),
and organic matter composed of humic and fulvic acids. Organic matter
is not a significant component of the sediments of the Ranegras Plain basin and will not be discussed in this thesis.
Tamura (1972) described three types of ion exchange on minerals:
(1) isomorphic substitution in octahedral layers, (2) isomorphic substi-
tution in tetrahedral layers, and (3) ionizable ions present at the edges
of clay particles and on the surfaces of the hydrous sesquioxides. Ion
exchange due to isomorphism is constant over a wide range of pH. Ion
exchange due to ionization is a function of pH and total ion concentra-
tions. The third category of ion exchange contributes 5 percent of the
adsorption in montmorillonite and vermiculite and 100 percent of the
adsorption in the sesquioxides.
Strontium Adsorption on Clays
A number of authors have discussed the adsorption of strontium
on clays. Thornthwaite, Mather, and Nakamura (1960) described the slow movement of radiostrontium in soils of high clay content. The rate of movement is dependent on the cation exchange capacity, the soil pH, and 135
the leaching efficiency of the infiltrating water. Jackson et al.
(1980) demonstrated that strontium was preferentially adsorbed on the
fine fraction (predominantly clays) and the coarse fraction (micaceous
minerals) of the Chalk River aquifer sediments.
Ion Exchange Equilibria
According to the Gouy double layer theory, divalent cations are
more strongly adsorbed than monovalent ions (Stumm and Morgan, 1981).
This accounts for the selective adsorption of calcium and strontium over
sodium and potassium. The model predicts the observed behavior that the
selectivity of adsorption decreases with increasing ion strength of the
solution. The Hofmeister series, listed below, predicts that for most
clays the ion with the larger hydrated radius tends to be displaced by
the ion of smaller hydrated radius.
Ba2+ > Sr 2+ > Ca2+ > Mg2+ (6.24)
The exchange of two divalent ions is represented by the following equation:
A-clay + B 2+ = B-clay + (6.25)
The exchange equilibrium for two cations is represented by:
a a A-clay A2+ — KAB — (6.26) a a B-clay B 2+ 136 where a and a represent the activities of A2+ and B 2+ on the A-clay B-clay exchange sites, a and a are the activities in solution, and KAB is A2+ B2+ the exchange constant. If the concentration of A2+ adsorbed on the clay and in solution are small compared to the total concentrations of cations in solution and the cation exchange capacity of the clay (CEC), the equation may be written (Dreyer, 1982):
CEC m = KAB — m (6.27) A-clay M A2+ where:
m = concentration of A2+ adsorbed on the clay (meq/g) A-clay
CEC = cation exchange capacity of the clay (meq/g)
M = total concentration of cations in solution (meq/l)
m = concentration of A+ in solution (meq/l) A2+
The concentration of adsorbed strontium is directly proportional to the cation exchange capacity and the concentration of the strontium in solu- tion. The equation can be simplified into the following expression:
M =K M (6.28) A-clay A- where Kd is the distribution coefficient. Kd is a function of the other ions in solution. A distribution coefficient calculated for a particular ion, solution, and clay cannot be used for calculations in- volving other solutions or clays. 137
The equilibrium equation is more complicated for the exchange of monovalent and divalent ions.
2 A-clay + C 2+ C-clay + 2 A
a a C-clay C 2+ AB ---- (6.30) 2 2 a a A-clay A+
The distribution coefficient will, however, be defined by an equation similar to that for the exchange of two monovalent ions.
(6.30) C-clay
Wahlberg et al. (1965) demonstrated that the exchange of tracer- level concentrations of strontium on the minerals kaolinite, montmoril- lonite, and illite from solutions with one competing ion (sodium, calcium, magnesium, or potassium) was adequately defined by the mass- action equilibrium equation. As expected, the adsorption was greatest from sodium solutions and the least from calcium solutions. If the competing ion concentrations are constant, the value for Kd is constant over a range of aqueous strontium concentrations up to 10 -4 N
(4.4 mg/1). An additional study of the adsorption of strontium on kaolinite and montmorillonite with two of the competing cations demon- strated that the exchange adsorption could be predicted from the results of the one competing ion investigation (Wahlberg and Dewar, 1965). 138
Strontium Adsorption on Sesouioxides
Freshly prepared iron and aluminum hydrous oxide gels selec- tively adsorb traces of calcium and strontium from solutions containing up to 250,000 times more sodium (Kinniburgh, Syers, and Jackson, 1975).
The fraction of strontium and calcium adsorbed depends primarily on the pH. The variation of sodium concentration has only a small effect on the strontium and calcium adsorption. They observed a net release of approximately one hydrogen ion per each adsorbed divalent ion and a sharp increase in adsorption at pH 6.0 to 7.5 for the iron gel and pH
7.5 to 9.0 for the aluminum gel. In similar experiments with montmoril- lonite (Tamura, 1964) showed a marked decrease in the adsorption of trace quantities of strontium with increasing electrolyte concentration. pH Dependence of Adsorption on Clays
Numerous authors observed the pH dependence of strontium adsorp- tion by soils and clays: Rhodes (1957), McHenry (1958); Thornthwaite,
Mather, and Nakamura (1960); Kinniburgh, Syers, and Jackson (1975);
Tamura (1972); and Keren and O'Connor (1983). Rhodes (1957) observed that strontium adsorption by non-calcareous soils increases with pH and reaches a maximum at pH 10. The distribution coefficient increased linearly from pH 5 to pH 10 in that study. The greatest level of stron- tium adsorption in calcareous soils was found to occur between pH 8 and pH 10 and to decrease rapidly below pH 8.
The control of strontium concentrations in the groundwater of the Ranegras Plain basin by ion exchange is consistent with the strong pH dependence of strontium concentrations in groundwater (Figure 29). 139
This pH dependence may reflect both ion exchange and the solid solution of strontium in calcite.
Effect of HiRh Sulfate Concentrations on Strontium Adsorption
Bowman and O'Connor (1982) reported that the adsorption of strontium was higher in the slightly-complexing chloride system than the highly-complexing sulfate system at the same total strontium concentra- tion. The data supported the hypothesis that the SrSO4 ° complex is not adsorbed. Differences in the adsorption isotherms between the two systems disappeared if free Sr 2+ activities were used instead of concen- trations.
These data suggest that the positive correlation of strontium and sulfate in the Ranegras Plain basin may be due not only to the release of strontium as a trace constituent during the dissolution of gypsum, but also to the inhibiting effect that elevated sulfate concen- trations have on the adsorption of strontium on clays.
Estimate of Adsorbed Strontium on Montmorillonite at the Ranegras Plain Basin
This section presents an estimate of the strontium adsorbed on montmorillonite clay in the Ranegras Plain basin. These calculations are based on assumptions that are approximate, and the results are, therefore, considered order-of-magnitude estimates of the adsorbed strontium concentration on montmorillonite in the Ranegras Plain basin.
Wahlberg and Dewar (1965) determined the distribution coefficients used in these calculations by measuring the adsorption of strontium onto sodium montmorillonite from solutions of varying concentrations of cal- 140 cium and sodium prepared as the chloride salts. Due to the complex solution chemistry and variety of exchange surfaces present in real systems, the use of mass-action equations and distribution coefficients to project strontium adsorption can be misleading (Johnson and Gillham,
1984). The distribution coefficient is therefore generally considered an empirical parameter which should be experimentally determined at individual study areas.
The assumptions used in these calculations are listed below:
1. The aquifer clays are composed of montmorillonite.
Robertson (1986) reports that montmorillonite constitutes the
great majority of clays in the alluvial basins of the southern
Arizona. The component of adsorption due to sesquioxides and
silicate minerals will not be included in these calculations,
although it may potentially be a significant portion of total
strontium adsorption in the aquifer sediments.
2. Calcium and sodium are the only major cations in solution.
Calcium and sodium account for over 90 percent of the
milliequivalents of cations in most well samples from the
Ranegras Plain basin. Potassium and magnesium would not
expected to compete significantly for adsorption sites.
3. Chloride is the only anion present in solution.
This assumption does not agree with the groundwater analyses
from the Ranegras Plain basin. Chloride generally accounts for
50 percent or less of the total milliequivalents of anions in 141
solution. Elevated sulfate concentrations are expected to
reduce the concentration of adsorbed strontium.
4. The strontium concentration in groundwater is controlled by
cation exchange with clays. Other mechanisms such as the solid
solution of strontium in gypsum and calcite are not included in
the analysis.
This author calculated the concentration of adsorbed strontium on clays for three individual wells samples that contain elevated stron- tium concentrations (Wells No. 15, 21 and 36) and for the basin average water quality. The results of the calculations are listed in Table 9.
These three wells were selected because the sodium and calcium concen- trations in the groundwater most closely represented the concentrations used for the experimentally determined distribution coefficients. The specific sodium and calcium concentrations used for the experimental determination of the distribution coefficients and the groundwater anal- ysis are listed in Table 9. Wells No. 15 and 36 contain high total dissolved solids due to the dissolution of evaporites. Well No. 21 is in a recharge zone on the western side of the basin.
The calculated strontium concentrations on montmorillonite asso- ciated with Wells No. 15 and 36 are 0.021 meq/g (920 ppm) and 0.103 meq/g (4500 ppm), respectively. The higher calculated adsorbed stron- tium concentration for Well No. 36 is due to the lower calcium content in the groundwater from this well. The distribution coefficient at 100 142
Table 9. Calculation of adsorbed strontium on montmorillonite clays.
(a) Experimental (b)
Groundwater Analysis Conditions SrX
Groundwater Ca Na Sr Sr Ca Na K Sample (mg/l) (mg/L) (mg/t) (normality) (mg/l) (mg/l) d (meq/g) (ppm)
-5 Basin Average 54 236 1.25 2.85 x 10 100 230 1100 0.031 1360
-5 Well No. 15 260 200 4.1 9.49 x 10 230 230 230 0.021 920
-5 Well No. 36 76 340 4.1 9.49 x 10 100 230 1100 0.103 4500
-5 Well No. 21 89 93 4.4 1.07 x 10 100 115 1900 0.203 8900
(a) Experimemtal conditions used to determine K (Wahlberg and Dewar, 1965) d (b) SrX = K [Sr] d
SrX = quantitiy of strontium adsorbed on the clay in meq/B
K = distribution coefficient d
[Sri = normality of strontium in groundwater 143 mg/1 calcium is only one-fifth that of the coefficient at 230 mg/1 when the sodium concentration is 230 mg/l.
The calculated strontium concentration on montmorillonite asso- ciated with Well No. 21 is 0.180 meq/g (8900 ppm). The high calculated strontium content adsorbed on clay results from the high distribution coefficient at the relatively low sodium and calcium concentrations.
The adsorbed strontium content on montmorillonite calculated for the basin average water chemistry is 1360 ppm. This value represents only a relative estimate of strontium adsorption in the basin.
The calculated values of adsorbed strontium on clays in the
Ranegras Plain basin are considerably higher than the few available published values for adsorbed and total strontium. Singer and Navrot
(1973) reported 22 to 191 ppm strontium in clays which are the weather- ing product of basalt scoriae, basaltic tuff-lapilli, and olivine basalt. The strontium content of the basalts varied from 405 ppm for the basalt scoriae to 987 ppm for the olivine basalt. Short (1961) reported on the trace metal content of residual soils developed from granodiorite, basalt, granite, metamorphosed andesite. The strontium concentration of the clay fraction was 88 to 192 ppm for the granodio- rite, 30 to 51 ppm for the basalt, and 48 to 133 ppm for the meta- andesite. The highest strontium content of the residual minerals was found in the silt fraction.
Odum (1957b) analyzed the acid-extractable fraction of samples of argillaceous lake sediments from arid basins. These samples may be representative of sediments from the Ranegras Plain basin. The acid- 144 extractable fraction represents the total strontium adsorbed on clays, sesquioxides, and silicate minerals, in addition to that present in acid soluble minerals such as gypsum and calcite. Strontium concentrations in lake sediments calculated from Odum's (1957b) published percent cal- cium and Sr/Ca values ranged from 20 to 496 ppm for the Carson sink in
Nevada, 140 to 760 ppm for arid lakes in Tibet, 400 ppm for the Pyramid
Valley Swamp in New Zealand, and 31 to 212 ppm for the Great Salt Lake,
Utah. These values are generally lower than the estimates of strontium adsorbed on clays at the Ranegras Plain. This discrepancy may be due to inaccuracies in the adsorbed strontium estimates or the fact that the
Ranegras Plain contains higher aqueous concentrations of strontium than at the locations of the other published values.
The analysis indicates that significant quantities of strontium may be adsorbed on the clays of the aquifer sediments. Appreciable concentrations of strontium could also adsorb onto sesquioxides and primary aluminosilicate minerals. Strontium was likely concentrated in clays during their formation in the playa environment. Precipitated calcite and gypsum may have contained even higher strontium concentra- tions. In the present environment, clays may act to reduce the aqueous strontium concentration by the processes of adsorption and cation ex- change, particularly when the pH is greater than 8. The dependence of aqueous strontium concentrations on pH supports the hypothesis of clay adsorption as an important controlling mechanism for the aqueous stron- tium geochemistry, particularly in those areas of the basin that are undersaturated with respect to calcite. CHAPTER 7
ANALYSIS OF POTENTIAL STRONTIUM SOURCE ROCKS AND WELL CUTTINGS
This chapter describes the chemical analysis of (1) represen- tative rocks that are potential sources of strontium from the mountains surrounding the Ranegras Plain basin and (2) well cuttings from two wells in the basin. The well cuttings analyses are used to further test the hypothesis of solid solution of strontium in calcite and gypsum and to calculate the percent strontium in groundwater originating from gypsum dissolution. The variation of the Sr/Ca molar ratios with depth indicates a period of closed drainage for the basin.
Analysis of Source Rocks
A number of rock types that represented potential strontium source rocks were analyzed for strontium by x-ray fluorescence spectro- scopy (whole rock analysis). The acid-extractable fraction of the rock samples was analyzed for both strontium and calcium by atomic absorption spectroscopy. Sample preparation procedures and analytical procedures are described in Appendix C. The x-ray fluorescence values represent total strontium. The acid-extractable fraction contains strontium and calcium contained in acid-soluble minerals such as calcite and gypsum, adsorbed calcium and strontium on residual clay and mineral surfaces, and minor contributions from silicate minerals.
145 146
Samples of rock types selected for chemical analysis were sus-
pected major sources of strontium in the basin. The rock types that
were analyzed are andesite from the Bouse Hills, Quaternary basalt from
the vicinity of Vicksburg and Brenda, and metamorphosed Mesozoic lime-
stone and gypsum from the Plomosa and Granite Wash Mountains. In addi-
tion, a surface exposure of caliche and the weathered rind from an
andesite boulder in the vicinity of Brenda were analyzed for strontium.
The sample locations are shown on Figure 39. The results of these anal-
yses are summarized in Table 10. The Sr/Ca molar ratios presented in
Table 9 and discussed in the text represent the moles of strontium per
1000 moles calcium.
Of those rock samples analyzed, the highest strontium concentra-
tions were in the basalt located near the towns of Vicksburg (528 ppm)
and Brenda (510 ppm). The highest strontium concentration in ground- water in the Ranegras Plain basin (4.4 mg/1) was in a sample from Well
No. 21 near Brenda, but water from wells located on the eastern side of
the basin near the Vicksburg basalt (Wells No. 10 and 11) contain stron-
tium in concentrations less than 0.20 mg/l. This difference is likely
due to the much lower pH of groundwater from Well No. 21 compared to
Wells No. 10 and 11. The andesite from the Bouse Hills was expected to have relatively high strontium concentrations, since the majority of the high strontium areas occur in the northern part of the basin, adjacent
to the Bouse Hills; however, the strontium content of the andesite was only 244 ppm. The source of strontium in that part of the basin may be 147
0 5
SCALE IN MILES
• Potential Source 3 Rock Sample Number
Figure 39. Locations of strontium source rock samples and well cuttings samples. 148
Table 10. Chemical analyses of potential strontium source rocks.
X-RAY FLUORESCENCE ACID EXTRACTABLE ANALYSIS Sr/Ca Ratio
Sample Sample Percent No. Description Sr Method Sr Ca Insoluble (a) (b) (Pqn) (ppm) (X) Residue (wt/wt) (molar ratio)
Ca Caliche-Plomosa 119 40.6 43.3 0.293 0.134 Ka Andesite-Bouse 244 1 Otb-Vicksberg 528 2 Basalt-Brenda 510 3 Andesite rind 374 39.9 25.4 0.937 0.429
4 Limestone 216 36.5 5.2 0.592 0.271 5 (Plomosa Pass) 200 224 37.7 17.9 0.594 0.272 6 320 22.0 93.3 1.450 0.663 7 207 52.1 39.1 0.397 0.182 8 145 36.3 5.2 0.399 0.183 9 347 34.7 7.5 1.000 0.457 10 169 23.7 86.0 0.713 0.326 11 228 26.2 89.3 0.870 0.398 12 158 16.8 92.1 0.940 0.430 13 336 33.6 7.3 1.000 0.457 16 169 40.4 9.4 0.418 0.191
21 Limestone 152 41.1 3.8 0.370 0.169 22 (Granite Wash Mtns.) 396 25.7 87.5 1.540 0.704 23 107 44.2 0.0 0.242 0.111 24 193 39.6 25.8 0.487 0.223 25 142 130 28.9 8.1 0.450 0.206
G-E Gypsum-Granite Wash 74 D 109 26.7 0.0 0.408 0.187 Mountains K 112 0.0 0.419 0.192 G-W Gypsum-Plomosa 60 D 80 25.6 0.0 0.312 0.143 Mountains K 112 0.0 0.437 0.200
a Sr/Ca Ratio (wt/wt) = grams strontium/1000 grams calcium
Sr/Ca Molar Ratio = moles strontium/1000 moles calcium
D - direct analysis of acid extract
K - analysis of acid extract by method of known additions 149
due to the olivine basalt and weathered volcanic tuffs which occur in
that area.
The relatively high strontium concentration (374 ppm) and Sr/Ca molar ratio (0.428) of the andesite rind indicates that the strontium in
the andesite accumulates in the acid soluble fraction of the weathering products and is high enough to be a significant source of strontium in
the groundwater.
The limestone samples from the Plomosa and Granite Wash Moun-
tains contain relatively low strontium concentrations. Limestone and
gypsum occur within a sequence of Paleozoic and Lower Mesozoic meta-
sedimentary rocks in both mountain chains (Reynolds et al., 1986).
Samples were taken at various locations along the stratigraphic sequence
in both mountain chains.
In the Plomosa Pass area, the strontium concentration of the metamorphosed limestone ranged from 145 to 347 ppm and averaged 229 ppm
(Table 10). The Sr/Ca molar ratio ranged from 0.182 to 0.663 and aver- aged 0.348. This ratio is considerably less than the average Sr/Ca molar ratio of 12.0 for groundwater samples from the basin (Table 1).
The limestone in the Granite Wash Mountains ranges from 130 to 396 ppm and averages 196 ppm. The Sr/Ca molar ratio of the Granite Wash lime- stone samples averages 0.282. These strontium concentrations and Sr/Ca molar ratios indicate that the limestones are not the primary source of strontium in the groundwater basin.
The gypsum deposits in the Plomosa and Granite Wash Mountains were suspected to be significant source rocks of strontium in the 150 groundwater and sources of the gypsum accumulations found in well cut- tings in the Ranegras Plains basin. The strontium concentration of the gypsum was, however, relatively low, ranging from 60 to 112 ppm
(Table 10). The strontium concentrations determined by x-ray fluo- rescence (whole rock analysis) are approximately 50 to 75 percent of those values determined by atomic absorption spectroscopy. The Sr/Ca molar ratios of the gypsum samples range from 0.143 to 0.200. These strontium concentrations and Sr/Ca molar ratios are considerably less that those for gypsum samples from well cuttings in the basin, thus indicating that the Plomosa and Granite Wash Mountain gypsum deposits are not major sources of strontium in the groundwater basin.
The caliche sample was a near surface deposit uncovered by soil erosion on the bajada directly east of the Plomosa Mountains (Figure 39).
The low strontium concentration (119 ppm) and Sr/Ca ratio (0.134) are not surprising, since the approximately 4 feet of soil and sediment overlying the caliche does not represent a source of strontium high enough to produce high strontium calcite.
Analysis of Well Cuttings
The acid-extractable fraction of well cuttings from two wells in the Ranegras Plain basin was analyzed for calcium, strontium, and sul- fate. Well cuttings from Well No. 7 [Well B(3-15)2dab, identified on the well log in Appendix A as Lab No. 2621) and Well No. 64 [Well B(7-17)
15dcd, identified on the well log as Lab No. 64 ] were obtained from the Arizona Bureau of Geology and Mineral Technology, Tucson, Arizona.
These well cuttings were washed prior to storage at the Bureau and thus 151 do not contain the clay fraction. Results may, therefore, be somewhat biased. Well logs for Well No.7 and Well No 64 are in Appendix A. The results of the chemical analyses are summarized in Table 11.
Well No. 64 is at the base of the Bouse Hills in the northwest corner of the basin (Figure 39), an area of high groundwater strontium concentrations (2 to 4 mg/1). The well log (Appendix A) shows that the major constituents of the cuttings are rhyolite, felsite, quartz, and granite, with minor amounts of magnetite, calcite, and olivine. No water sample was available from this well.
Well No. 7 is in the center of the southern half of the basin
(Figure 39) in an area of low groundwater strontium concentrations (0.20 mg/1). Washed or partially washed samples are available every 20 feet from 140 to 960 feet. The cuttings samples consist predominantly of andesite, welded tuff, and rhyolite with minor amounts of sandstone, gypsum, and limestone. The well log is in Appendix A. A chemical anal- ysis of groundwater is available for this well.
Well No. 7
Representative well cutting samples from Well No. 7 and samples of gypsum contained in those cuttings were analyzed. The available well cutting samples were combined into depth intervals ranging in thickness from 20 to 80 feet. Smaller intervals were used where higher strontium concentrations were encountered. Individual gypsum crystals selected from the cuttings at depths of 740, 780, 820, and 860 feet were analyz- ed. The concentration of calcium, strontium, and sulfate in the well cutting samples for the intervals from 150 feet through 480 feet is
152
Table 11. Chemical analyses of well cutting samples.
Analyses of Aqueous Analyses of Acid-extractable Wt. Acid Acid Extract Fraction of Samples (a) (b) Sample Depth Wt. Soluble Percent Dilution Sr/Ca Sr/Ca Sr/Sulfate Sulfate/Ca No. Interval Sample Fraction Insoluble Volume Ca Sr Sulfate Ca Sr Sulfate Ratio Molar Molar Molar (feet) (g) (g) Residue (mis) (mg/1) (mg/1) (mg/1) (%) (PPm) (%) (wt/wt) Ratio Ratio Ratio
Well No. 6, B(3-15)2dab
1.9388Cuttings 150-180 (c) (c) 100 709 0.68 0 (c) (c) (c) 0.96 0.44 - 0.000 200-280 1.9210 (c) (c) 100 407 0.50 2 (c) (c) (c) 1.23 0.56 0.3 0.002 300-380 2.0451 (c) (c) 100 265 0.37 5 (c) (c) (c) 1.40 0.64 0.08 0.008 400-480 1.9655 (c) (c) 100 298 0.39 3 (c) (c) (c) 1.31 0.60 0.1 0.004 500-580 2.0492 0.1746 91.5 100 498 0.25 0 28.5 143 0.000 0.50 0.23 - 0.000 600-680 2.0940 0.1415 93.2 100 391 0.48 12 27.6 339 0.848 1.23 0.56 0.044 0.013 700-720 0.9540 0.2340 75.8 100 502 1.57 700 21.5 671 29.915 3.13 1.43 0.0025 0.582 740-760 0.9789 0.2622 73.2 100 589 1.82 840 22.5 694 32.037 3.09 1.41 0.0024 0.595 780-800 1.0457 0.3114 70.2 100 639 3.00 1120 20.5 963 35.967 4.69 2.15 0.0029 0.731 820-840 1.0556 0.2435 76.9 100 581 2.71 600 23.9 1130 24.641 4.66 2.13 0.0050 0.431 860-880 1.0312 0.1224 88.1 100 296 1.08 55- 24.2 882 4.493 3.65 1.67 0.0215 0.078 900-920 2.1979 0.1425 93.5 100 392 1.07 12 27.5 751 0.842 2.73 1.25 0.0978 0.013 940-960 2.0071 0.1110 94.5 100 285 0.33 12 25.7 297 1.081 1.16 0.53 0.0301 0.018
24.6Average 527 2.29 1.05 0.054
0.1650 <0.1Gypsum 740 (d) 250 1.62 0.16 NA 24.5 242 NA 0.92 0.42 - 0.1924780 (d) <0.1 100 4.66 1.03 NA 24.2 535 NA 2.21 1.01 (d) <0.1 100 4.60 1.11 NA 23.9 577 NA 2.41 1.10 0.1318820 (d) <0.1 250 1.32 0.22 NA 25.0 418 NA 1.67 0.76 - 0.1269860 (d) <0.1 250 1.35 0.15 NA 26.6 295 NA 1.11 0.51 - -
Average 24.8 413 1.66 0.76
Well NO. 64, B(7-17)15dcd
Cuttings 10-45 2.9974 0.1027 96.6 214 0.72 6 20.8 701 0.584 3.36 1.54 0.1 0.012 4 50-80 2.9955 0.1500 95.0 451 1.12 30.1 747 0.267 2.48 1.14 0.3 0.004 90-110 3.1195 0.2937 96.0 962 1.65 4 32.8 562 0.136 1.72 0.78 0.5 0.002
(a) Sr/Ca Ratio (wt/wt) - grams strontium/1000 grams calcium (b) Sr/Ca molar ratio - moles strontium/1000 moles calcium (c) Wt. acid soluble fraction and residue could not be determined, since magnetite contained in cuttings samples adhered to magnetic stirring bar. (d) Gypsum was dissolved in distilled water. No measureable residue was left after the dissolution of the gypsum samples.
NA - Not analyzed 153 not reported in Table 11. Magnetite present in the samples adhered to the magnetic stirring bar used during the dissolution procedure, thus preventing an accurate measurement of the sample weight after the acid dissolution procedure. It was possible, however, to calculate the Sr/Ca molar ratios for the acid-extractable fraction for samples in this interval. The strontium concentrations in the acid-extractable fraction of the cuttings range from 143 to 1110 ppm (Figure 40). The highest concentrations occur in the gypsiferous interval at a depth of 700 to
860 feet.
The percent calcium of the acid-extractable fraction of the well cuttings ranges from a low of 20.5 percent to a high of 28.5 percent.
Pure gypsum has a calculated calcium content of 23.3 percent. The per- cent calcium of cutting samples in the gypsiferous interval range from
20.5 and 23.9 percent, comparable to that of gypsum. The cutting sampl- es above and below this interval contain higher percentages of calcium
(from 24.2 to 28.5 percent), indicating that the acid-extractable frac- tion of those intervals may contain more calcium in the form of calcite or as exchangeable calcium on clays. Pure calcite has a calculated calcium content of 40.0 percent. The individual gypsum samples contain an average of 24.8 percent calcium, close to the calculated percent calcium for gypsum.
The Sr/Ca molar ratio for the cuttings of Well No. 7 ranges from
0.230 to 2.15. The highest ratios occur in the gypsiferous interval, thus indicating that the gypsum may be the primary source of strontium in the groundwater from this well (Figure 40). 154
PERCENT CALCIUM FROM GYPSUM (CALCULATED)
10 20 30 40 50 60 70 80 i I I l
100 - EXPLANATION:
• SR CONC. IN ACID-EXTRACTABLE FRACTION OF WELL CUTTINGS
200 - - • SR CONC. IN GYPSUM
— SR/CR MOLAR RATIO(a)OF ACID- EXTRACTABLE FRACTION OF WELL CUTTINGS
300 - - -• — PERCENT CALCIUM FROM GYPSUM (CALCULATED)
• DEPTH INTERVAL OF SAMPLE
400 -
/
500-J T
•
800 -
700 -
800 -
900 -
1 1000 o 200 400 STRONTIUM CONCENTRATION (ppm)
(a) SR/CA MOLAR RATIO = MOLES SR/1000 MOLES CA
Figure 40. Strontium concentrations and Sr/Ca molar ratios of the acid- extractable fraction of well cutting samples from Well No. 7 as a function of depth. 155
The Sr/Ca molar ratio of the cuttings in the gypsiferous inter-
val is approximately 2 to 3 times higher than the ratio in the gypsum at
each depth interval. Therefore, sources other than the gypsum are
responsible for the total strontium concentrations in the cuttings at
these intervals. Strontium concentrations adsorbed on sediments or
contained in calcite must be higher than that contained in the gypsum.
The percentage of calcium in the cuttings originating from the
dissolution of gypsum was calculated in Table 11 as the sulfate/calcium molar ratio and is shown on Figure 40. The calculation assumes that all
sulfate in the acid extract of the cuttings originates gypsum dissolu-
tion. The percent calcium from gypsum in the acid-extractable fraction
ranges from 43 to 59 percent in the gypsiferous interval and from 0 to
2.8 percent in the underlying and overlying depth intervals. The
remainder of the calcium at each depth originates from calcite, cation
exchange, or the weathering of silicate minerals.
The sulfate concentrations may be low, since some sulfate is
converted to bisulfite at the acidic pH values used for the acid extrac-
tion of the sediments. The effect of this error would be to lower the
sulfate/calcium ratio of the samples. This error would not affect the
location and relative magnitude of the gypsiferous interval.
Well No. 64
Representative well cutting samples from Well No. 64
[B(7-17)15dcd] were analyzed for three depth intervals: 10 to 45 feet,
50 to 80 feet, and 90 to 110 feet (Table 11). The strontium concentra- tion of the acid-extractable fraction is relatively high (701 to 156
747 ppm), as expected, since elevated concentrations of strontium occur
in the groundwater of this area. The low sulfate content of the acid- extractable fraction (0.14 to 0.58 percent) and the absence of gypsum in
the well cuttings demonstrate that gypsum is not responsible for the high strontium concentrations in the well cuttings. The percent calcium
in the acid-extractable fraction ranges from 20.8 percent at 10 to 45 feet to 32.8 percent at 90 to 110 feet. The higher calcium content at depth correlates with the occurrence of calcite cement in the well cuttings.
The Sr/Ca molar ratio ranges from 1.54 (10 to 45 feet depth) to
0.78 (90 to 110 feet depth). These values are lower than that in the gypsiferous interval of Well No. 7, but considerably higher than the nongypsiferous interval of Well No. 7, indicating that the strontium in calcite and adsorbed on clays in Well No. 64 at depths less than 110 feet is present in concentrations considerably greater than in Well No.
64. This suggests a nearby source of strontium in the Bouse area, most likely the olivine basalt, volcanic tuffs, and hydrothermal deposits.
Strontium in the Sediments of Closed Lake Basins
Elevated Sr/Ca ratios of lake sediments have been correlated with an arid climate and closed drainage. Analysis of sediment cores from two arid lakes, the Great Salt Lake and Pangong Tso, Tibet (Odum
1957b) indicated that Sr/Ca molar ratios may increase with increasing aridity of climate.
Hutchinson, Wollack, and Setlow (1943) and Odum (1957a, 1957b) showed that the Sr/Ca molar ratio and calcium content of sediments of 157
closed lakes was higher than in those of open lakes for cases in which
the chemical natures of drainages were similar. Ahrens (1945) noted
that of the clays analyzed in his studies, saline lacustrine clay from
Gilbania, Sinai had the highest strontium content.
Odum (1957a, 1957b) proposed that in open lakes, the rate of calcium deposition in the sediments is less than the rate of calcium
inflow. The Sr/Ca ratio of the water would be expected to rise due to the exclusion of strontium relative to calcium during calcareous deposi- tion; however, the outflow of water from the lake would maintain the
Sr/Ca ratio at a maximum value. In closed lakes the Sr/Ca ratio of the lake water would continue to rise during the precipitation of calcite, aragonite, and gypsum, thus resulting in an increase of the Sr/Ca ratio of these minerals and for adsorbed strontium and calcium on clays.
The increase of the Sr/Ca ratio of the acid-extractable fraction of the well cuttings from Well No. 7 from a depth of 950 feet to 800 feet indicates a period of closed drainage (Table 11, Figure 40). The presence of gypsum over this interval further supports that conclusion.
The Sr/Ca molar ratio for the gypsum increases from 860 feet to 780 feet.
The decrease of the Sr/Ca ratio for the acid-extractable frac- tion of the well cuttings from approximately 780 feet to 540 feet may represent a period of increased water inflow into the playa, or possible outflow of water from the basin (transition from a closed basin to an open basin). 158
Solid Solution Calculations for Well No. 7
Chemical analyses for both groundwater and well cuttings were completed for Well No. 7; therefore, these data may be used to compare the predicted Sr/Ca molar ratio in groundwater using solid solution theory with the actual groundwater analysis.
Well No. 7 is saturated with respect to calcite (S.I. = -0.096), slightly undersaturated with respect to aragonite (S.I. = -0.230), and undersaturated with respect to gypsum (S.I. = -1.949), even though gyp- sum is present in the well cuttings for 180 feet of the total 670 feet of saturated interval in the well.
Table 12 summarizes the calculated Sr/Ca molar ratios for the groundwater from Well No. 7 assuming solid solution of strontium in calcite, aragonite, and gypsum. The Sr/Ca molar ratios were calculated using published partition coefficients for each mineral and the average
Sr/Ca molar ratio of the well cutting samples from this well. It is assumed that all strontium in the groundwater is derived from the solid solution of strontium with each respective mineral. The calculated
Sr/Ca ratio for the groundwater assuming solid solution with calcite
(7.50) agrees within 2 percent with the average Sr/Ca ratio for the actual groundwater analysis (7.62). The calculated Sr/Ca ratio for the groundwater assuming solid solution with gypsum (5.83) is 22 percent less than the actual ratio for the groundwater. The calculated Sr/Ca ratio for the groundwater assuming solid solution with aragonite (1.02) is approximately 7.5 times less than the average ratio for the sedi- ments. The close agreement of the calculated Sr/Ca ratio for the 159
Table 12. Calculated Sr/Ca molar ratios for groundwater from Well No. 7 assuming solid solution of strontium with calcite, aragonite, and gypsum.
(a) Sr/Ca Molar Ratio of Groundwater Saturation Index of Partition Groundwater with Coefficient (b) (c) Mineral Respect to Mineral D Calculated Measured (d) Calcite -0.096 0.14 7.50 7.62 (e) Aragonite -0.230 1.03 1.02 7.62 (f) Gypsum -1.949 0.18 5.83 7.62
(a) Sr/Ca Molar Ratio - Atoms strontium/1000 atoms calcium (b) (Sr/Ca) - 1/D (Sr/Ca) groundwater mineral
(Sr/Ca) - Mean value of Sr/Ca molar ratio for all depth mineral intervals of Well No. 7 from Table 10
- 1.05 (c) Measured Sr/Ca molar ratio for groundwater from Well No. 7 (d) Kinsman (1969) (e) Purser (1973)
(f) Kinsman and Holland (1969) 160 groundwater assuming solid solution with calcite and gypsum suggests that this is a reasonable mechanism controlling the concentration of strontium in the groundwater extracted by Well No. 7.
The distribution coefficient for calcite and gypsum are similar in value. Therefore, if the measured strontium concentration in the groundwater is due to solid solution of both minerals, the calculated
Sr/Ca ratio for the sediments is not greatly affected.
The groundwater from Well No. 7 contains 160 mg/1 sulfate (3.33 meq/l) and 12 mg/1 calcium (0.59 meq/l). The molar concentration of sulfate is more than 5 times higher than that of calcium. If the sul- fate in the groundwater is derived entirely from gypsum dissolution, then 82 percent of the gypsum-derived calcium has been adsorbed on clays
(in exchange for sodium) or has precipitated as calcite. Due to the selective adsorption of strontium over calcium, the effect of cation exchange would be to lower the Sr/Ca ratio in the groundwater relative to that predicted by solid solution of strontium in calcite and gypsum.
Summary
Rocks that were considered potential sources of strontium from the mountains surrounding the Ranegras Plain basin were analyzed for strontium and calcium, and cuttings from two wells in the basin were analyzed for strontium, calcium, and sulfate. Quaternary basalt con- tains the highest concentration of strontium (528 ppm) of the potential source rocks that were analyzed. Limestone and gypsum samples from the
Plomosa and Granite Wash Mountains are relatively low in strontium, averaging approximately 210 ppm and 100 ppm respectively. 161
The strontium concentrations of the acid-extractable fraction of the well cuttings are highest (up to 1120 ppm) in the gypsiferous interval of Well No. 7. Based on the analysis of individual gypsum crystals, the strontium contained in the gypsum accounts for only 1/3 to
1/2 of the total strontium in the acid-extractable fraction. The remainder of the strontium is derived from calcite dissolution and desorption of strontium from clays. In the gypsiferous interval, between 8 and 73 percent of the calcium in the acid-extractable fraction appears to originate from the gypsum.
An increase of the Sr/Ca molar ratio of the Well No. 7 cutting samples from a depth of 950 feet to 800 feet indicates a period of clos- ed drainage in the basin.
The Sr/Ca molar ratio for groundwater - from Well No. 7 calculated from the Sr/Ca ratio of the sediments agrees within 2 percent with the actual Sr/Ca ratio of the groundwater assuming solid solution with cal- cite, and within 20 percent assuming solid solution with gypsum. The close agreement supports the solid solution of strontium in calcite as a dominant geochemical control on the concentration of strontium in groundwater. CHAPTER 8
CONCLUSIONS
The Ranegras Plain groundwater basin is a fault-bound basin
filled with sediment eroded from the surrounding mountains. The basin
fill sediment exceeds 1,200 feet in depth and is composed primarily of a
coarse-grained piedmont facies at the basin perimeter and a fine-grained
playa facies in the basin center. The presence of gypsum at a depth of
700 to 920 feet implies internal drainage in the basin during the mid-
Miocene to mid-Pliocene.
Strontianite and celestite mineralization was not observed in
the Ranegras Plain basin; however, known deposits of strontianite and
celestite occur in southeastern California and western Arizona in asso-
ciation with evaporites, volcanic tuffs or lava flows, and hydrothermal
mineralization. All three rock types occur at the Ranegras Plain basin.
The Ranegras Plain basin contains groundwater of high total
dissolved solids characteristic of closed drainage basins. The chemical
type of groundwater is predominantly sodium chloride-sulfate. The high-
est mineral content occurs in the north-central and west-central part of
the basin in samples from wells that intersect the fine-grained facies.
The hydrogeochemistry of the basin is dominated by the dissolution of evaporites, primarily gypsum. Mineral saturation indices for ground- water samples indicate that the majority of the basin groundwater is
162 163 saturated with respect to calcite, illite, chalcedony, barite, and fluorite. Some wells produce groundwater saturated with respect to aragonite, dolomite, and gypsum. Mineral stability diagrams, mineral saturation indices, the high dissolved silica concentrations in ground- water, and the elevated pH of groundwater indicate that the weathering of silicate minerals significantly contributes to the groundwater chem- istry. Comparison of the chemical analyses of groundwater from nearby wells demonstrates that cation exchange of sodium for calcium is a dom- inant controlling reaction. Groundwater from significant recharge zones has comparably lower pH values, higher bicarbonate concentrations, and lower sodium content than the majority of groundwater in the basin.
Strontium concentrations in the groundwater range from 0.060 mg/1 in the southern part of the basin to 4.4 mg/1 in the north and west sides of the basin. The range of strontium concentrations approximates a log normal distribution. Strontium correlates positively with calci- um, sulfate, and total dissolved solids, suggesting that the dissolution of gypsum of which strontium is a trace component is the primary source of strontium in groundwater. Strontium concentrations are limited by the pH of the groundwater. The largest concentrations are associated with pH values less than 7.7. This relationship supports the concept of the solid solution of strontium in calcite and aragonite and is consis- tent with the known ion exchange behavior of strontium on clays and sesquioxides. The calculated Sr/Ca molar ratios for gypsum and aragon- ite using solid solution theory and groundwater analyses from the
Ranegras Plain basin agree with published values within a factor of 6. 164
Potential strontium source rocks from the surrounding mountains were analyzed. Quaternary basalt contained the highest strontium con-
centration of the samples analyzed. Concentrations of strontium in the
limestone and gypsum formations in the Plomosa Mountains and Granite
Wash Mountains are lower than those for basalt and andesite samples and
do not appear to be significant sources of the elevated strontium
concentrations in the basin groundwater.
Chemical analysis of the acid-extractable fraction of well cut-
tings from one well in the basin demonstrated that the highest strontium
concentrations are in a gypsiferous interval from 700 to 860 feet deep; however, the dissolution of gypsum in this interval accounts for only
1/3 to 1/2 of the total strontium in the acid-extractable fraction. The
remainder of the strontium was derived from the dissolution of calcite,
desorption from clays, and to a lessor extent from silicate hydrolysis.
The Sr/Ca molar ratio for groundwater from Well No. 7 calculated from
the Sr/Ca ratio of the sediments agrees within 2 percent with the actual
Sr/Ca ratio of the groundwater assuming solid solution with calcite, and within 20 percent assuming solid solution with gypsum. The close agree- ment supports the solid solution of strontium in calcite as a dominant
geochemical control on the concentrations of strontium in groundwater.
Based on the available information, the following scenario for
the hydrogeochemistry of strontium in the Ranegras Plain basin is pre- sented. No external drainage existed during the early formation of the basin. Gypsum, calcite or aragonite, and abundant clays accumulated in a playa environment. Weathering of Quaternary basalts and tuffs and 165
hydrothermal activity provided elevated concentrations of strontium
within the playa waters. Strontium concentrated in the gypsum and
authigenic calcite by solid solution and on the clays, silicate miner-
als, and sesquioxides by adsorption.
Dissolution of the evaporites dominates the hydrogeochemistry of
the basin today. Gypsum dissolution releases strontium, calcium, and
sulfate into the groundwater. The increased total dissolved solids of
groundwater in areas of evaporite dissolution inhibits strontium adsorp-
tion on clays due to the reduced selectivity of cation exchange from
solutions of high ionic strength and to the formation of the SrSO 4 °
species, which is not adsorbed due to its neutral charge. The decreased
adsorption further contributes to elevated strontium concentrations in
groundwater.
Hydrolysis of silicate minerals within the aquifer releases
dissolved cations into the groundwater and consumes acid. If the pH
increases sufficiently, calcite precipitation may occur. Strontium is
incorporated into the calcite by solid solution or as fluid inclusions.
Gypsum dissolution further induces calcite precipitation by the common
ion effect. Due to the difference between the partition coefficients of gypsum and calcite, the process of gypsum dissolution and calcite pre- cipitation enriches strontium in the groundwater.
Elevated strontium concentrations also occur in groundwater recharge zones, where the relatively low pH of the groundwater allows the dissolution of calcite containing strontium as a trace component. 166
In addition the low pH inhibits the adsorption of strontium on aquifer sediments. APPENDIX A
WELL LOGS
167
- ▪ - 1 ▪ • ▪
168
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169
o
g • O E ri ri .0 O kIC tn W 1.4 rt 40 .4 0 Q.0 0 ri •••J Cri 0 0U) .0 tO sC • Oh w 44 OP V) 0 o e • coo...") c o co 1004.4▪ W 404044.44) tr) 4) 4.4 P., C.) • VI al ›, 0 .4 IC W .0 .L.J z .c 1.4 4-, (00 04)10 VO ••-t 0. 0 O 0 • t•-• 7 44 10 0 th th 44 • 7 O-4" th 3 0 0 o cc • LL .c to, 0 r1 +.4 4 3 th H
ri ''00 0. ri 4-4 0 V • tO cic W IC 010V'• 4.404) 44044 O en O 7 (1) els•-(coocu O •-n ‘61 .40V 0440' 0 ,v 0 14 oœ Q41 21 %C.
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CiP
.0 0 g ri 117, crl h CO CO h 1.1 V' h 0 rn in Cl) in ill .P Ul •cr sr (-4 .4. sr Ln Ln sr dP
O • co ni) 0 0 N Cr, cc 0
dP ›. >4 >i >I >i >4 >4 >4 ION ION ri:/ ili 0 MS 0 it >e >4 >4 >4 >i 61\ 61\ 61N khl 61h1 61N 6iri 611,1 ON 417h1 ON rcl iN MIN 0h 0(--. 0\ 0\ 0\ 0\ 0\ 0\ 6. \ 61 \ 61 \ 61 \ 61 \ h h h h h h u r- c.D r-- c.7 r-- Q I-. c..D r.• 4 1.1 0k .0 4 .0 4 .0 .0 th >. N T 10k V1 1. fr, 14 cil 1.4 tn s4 (4k 4 k .0 k .0 1-1 .0 3-1 .0 H ..-1 ..-1 --t P•• ..-1 ›.. ..-t P... ri >1 ri >4 ri >1 10E-, 10E-, 10 E-, 00E-, 10E-, .14 Ill .W In .. ..44 .X .44 .sh x ri ri •r4 r ri 0 • G • 0 in O Ln c in c Ln c Ln c Ln t Lrl. ..sh Lr) ..0 Ln .sh Ir) .w in .-1 h ...-• h •..i ri ri ri ri ri 0 • G • G • 0 • a., Q. 0.. a. c. a. a. a. 0 ri h ri h r4 h r h ri h a. a. a. a. a. 0 IC' sr •ot sr sit sr sr sr sr sr sit sr sr •.--. -.._, -..... -..„ ....„ -..... -...„ -..., .L., IC ....., ...... , --... g Ln c Ln o Ln vl § Ln c Ln c Ln o Ln O 1.01,-) 0 Ln Ott) 0 Ln 3 3 X 3 3 3 3 3 3 0k 0k 0k 0k 0k 0k 0k 0k O k 0k 0k 0k 0k H >, 14 >, k>., HE-, HE-, H >, H >, HE-, HE-, k >, l•-n >. WE-, HE-, Cg OZ CA CO CO 03 00 0:1 CO 03 03 CO CO ul ul y) tg«) ul u") Ln ln tn Ln ul Ln Lri N h h h h h h h N h h h h r•a
CD 0 0 0 0 0 0 0 0 0 0 0 0 0 0) 0 rsi cr k0 CO 0 rsi sr 1/4.0 o3 0 r•; sr sr rO 0 sr cr sr •cr In Ln Ln L.1) tr) 1/40 1/40 1/40
• • ▪ ▪•
170
u) ..., rcl 0.4.' 0) 0 G 0 g .4 - 4 >' 4, a 0 io n 0 4J'4)4 ..- al 43 0 44 0 01 0 0 4-. 0 th Et 0) 0. I •••n C 0. E .• 0 0 0 4J 0) 4P A.) U C11 1.1 Ln 0 0 0 W I Q)) 0) 4., .0 ..-n s a is i‘i, ..4 0 0 0 44 ...4 g, ca ,or .. 0 CO 41 ...I 0 CIC +.+ 43 34 41 4-) › 0 0 ,1-1 >I 0 O 0 0 0 at 0 ri I., '4 W O EI 0 0 I* 4.• .0 0 E .4 v.I - '4 ... 01 Cl gh 3.1 E.• • C A t.) g 0 Ci. 0 0 4.) 0 .0 .34 0 ..4 34 0 0 ...) 0 0 0 ..., ..I .4 • • ✓ 34 0 U) 4, 0 • ..-• y o g a) .60 ..., .0 a 01. 0 0.) %.4 0) Cl 44 e s u) 44 N 0.1 g 0 O .0, 4.4 ,,... >. u ›,0 $...... , 0 0, ,0 0 0 . O4 cv c- aœco n) o., g- 4... 0, h '4 E IO 0 4.) CU 0, 44 V) 0 r4 4 0) 0 0 0) 100' 44 1.4 )4 (.) 0 0 0 44 cn ..-I r. 4., 0 0 o 4., ...• cv = ...I H 0 a Io L4 tD U1 4 03 . 0) U 14 g cn 4., WE --. v 0, co Es c• an CA U RI U dP 00 40 47 0 i4Uul 14 a. .4 CO 0 44 0 ••-i tr.. 0 4-1
Cri 00 40 0:3 In CO eV Ln i••• ✓.I : ZO 7:0 1.0, CO IV ...... ,. ...„...... „ Id.1 en r.I en .....
Ch Ch U) CI) Co tn X X
a, en en frC co ‘D r-4 1-4 r-1 (N I4 .
co kt:7 œ r CO en Cs rn c4 CN 454 lo ' en N rn
O •n•• O'. cr, 1-4 4-4 40 4^4 nc, Ln 44.4 Ln Ln dP >, >, 54 >.• >, >, >•, .0 .c 0 0 0 0 0 0 rcl 5,4_4 >4c4 cn ni In h 4.4(54 '4f_4 CGS- 10 •••... .4.4 '...... -4-4 *".. 4-I 4-1 '44_4 4.4 h 4.44_4 '44_4 '4f_4 ...... Q `.... CD -... 0 -... CD ',.. 0 "... 0 .... 0 ,.. '45 '45 G kr) C L.0 N s h h h h h CD 0 3 >. X T. >4 40 >41.0 .0 .0 4 .0 4 4 4 $.1 1.4 0f0).4 00/4 CO 0 0)44 0 14 0 14 CG', tri 34 E4. 0 34 44>' 4-, >, I. 1.1 ›, '4440.,?.1 1.1 61 44', O •,.1 >I ..0 >4 54>4 .r.1 D5 5>, 44>' .... ›. .0 .0 CO CD 04 CD Q>' Q>' X X ..se .s4 0, ul 14, in in Ln G an 0 Ln '. I)) O in .. Ln O sr, '65 u, ..-, • . • . . Ln In 0 -ri ..4 ...• .1-4 ...1 ...I ..-1 .4 r4 .4 454 ..) t-A 44 h 344 a, a4 a. a a. a I-a .-1 0 1 O 0 0 § X 54>' rti .0. .0. 0 0 0 0 0 o hi 0454 0C_4 0C_4 ta 0 ..., ^-.. 4.4(n 44(n 44 (n 34 rn 34 rn 34 -... 34 •••.. 34 .... 44'5.. I.4 ha 14 ni C4 '... Ln 0 Ln CO_'.. c0 --.- CO'. -- (OS-. 03 ',o. CO In Cg Ln 02 ill CO 441 Q"-.. CD 3 ,r) Ln in 4:1 40 in u'i A.; 044 044 .= .0 .c -c.' ..= .01-4 .04.. .0 )-1 .01-4 .0 .0 ).IP., 61›, 0 44 01.1 (t) 1•4 0)', cn w CG>' 0)3, CG>' 0) 54 0) 44 0 34 s-45. CO CO -•4 >• ...4 04 s-45, 4.4 >, ..-i >. .4-1 .4-4 94 4 .14 54 U') Ln V V V V V >40 5,0 5.0 5.0 '0 ,0 • ms ul ,,E 10 V in V in R:1 In 0 .-t 0 .-4 0 ,..4 (0 ,..1 V u) •@ in N: h 0) 0) a) a) 6 . 6, w 6, o a CO a a a CD 0 0 0 CO CO rn .0 ..) 0 0 0 0 0 0 0 o o o o o o C4 kr) CO C e`i 40. kt) œ 0 IN er V:, CO 0 Q) kr) %D h h h h h CO CO CO CO CO a, o 171
>1 D'_4 I crt D r-C 0 ..SC 0 0 O CO ri 0 G, 00 44. ...I 4 1-1 0 O4t 4) 4-+ 0) 40 0' 0 4 ••-t 0 4 '0 441 00 4.-4 0 40N0C/1 .0444 0 0.5 G g 40 V r-4 tO •-) 00 40 111.1 elP N W L4 4-4 0 ••• .4-I In X 10 040rn 40 0' .00.4.)464 4/1 CO > 10 0 0 NO 040 .0 (00 ••• 40 •,-+ OP V) '0 64 0 Z W tlf, 010 401-4 400' W 400 0 1)4040444.3 4.J 0 41 V I • 14 0. WI 44 140 In __4_cr-4 WIT:101311 4•1L ri .-4 U 0.-404 14 o41 0 40.0 40 Oc N W 0 1.4 14 1, 0 .44 tr) 4 0 ni 4 0 .14 U) U) 0 1, 1.4 -44440 0 (0W W f1:1 0 A.) el dP > 0 10 4.) 01 0 0 0.0 (0 40 W 40.0 1:4 41 44 W O .1.) •• I 0. 0' 1400 0 (44400 04 W 0,1-1 W'0'4_4 Q)4J Ç.4 01 41 01 C) W .14 •rol $.4 4 1.1 1.1 > 14 0) 0, 040 400 40 (0 4-' V V ...I 14 4.1 U) N(00)0) 00 4) 0 14 4.J 4) 4 .0 I. VO 14 0 ,41 0 4 .6.) tO U .4) (1) 40 .0V 00 0 En 0 .101, ,KC 01 1, 4040 0 14 )g 40.0 0 141 0 .4.4 0 4.) 4.1 144 44 ca 4) 0 0 $11 41 44V W 01 1-1 • u) .40 ••40 0 giP o•••n +.4 C1. 4,4 0 0 0 4 0 .0 E 0 40 (A in 41 X E. •••• fa vgaz tO p W - O 0, .0 • 0 • 40 -444 40(4-4 40 14.4 ,-.4144Q) (-4 v) r-- §1414 > a) .0 ciP V) ,--1 a, 0 , 0 I-I fd 1:11 14 (11 V r-f g > >•• CN • 0) - E. 0 4-3 -' X t441 .110 ZO .41. ..10 44 In ca •,-1 ....„, ....._ •..,_ 14 • Z r. 1,) n'l .-I O'W 4-4O /4 ti) 141 E-n 010 ,,.....rn lc E cr) 44 u 0 Z CO .4 W tO 1-i .4 3 14 4 ,4-1 z W (0 0 1.4 E Z a) ...a cri >, 0 CO 0 RI .0 0 0 4.4 4 1 4414 21 rl '0V WOO o- CD .0 W 0, > 40 .00400 (0 ,r, m csi 41 m al In 1440 0.0 4-1 CD 0 C./ (1) (.1 40.00j:a U de VI a) 0 64 14 w 0 V •0 En E O (0 •• KI Ul 440 in 4 (0 E (1) cr sr E 4) 4) CO G OP •• 0 14 (00 '0 p • V N On t•••. .-• W (0 -4 0.1 A 0 C.) 4.4 J.) 0 ...4 en -I en rk WO-._440'-40 dP 0 .0.0014 40 0 E-c OQ) 0 •• 4 V r. V400 • 0 E 0 -1-) 4.4 4) 0 (0 >4 110 11(004-00'PA 0 CO 40 40 400 O 10 40040.-4 CU 0 CO V) .14 tn 40 40 4-1 to 10 0 4 C.) 4-+ 0 ort (0 C.) (0 0 CG 0 4, 3.4 ••• 0 40.09-10V14-1 V 411.1 .41 14 jc 44W (00 1 1 CP • 1111 CO 40 1-1 W 06 0 L4 CS L) > 0E 0) '44. O 0 (1) n-t 0 'a 411 14.00.-4 o > '1-40'4146, 0 E .64 (4) 14 (4) 000 0, -440 r1 14 (.440 X r. 4 W .4 1.1 0) 0. .-4 ••• o g n:$ nof v 0, 0 ca .0 .61 On G1 $4 44 to tn W ra 0 A./ '-4Q)14-4 p, .71:1 U (...) .0 0 a/ 4, 0 0 0 6,Wexal C, 1 •*. 1/40 0.n (0 4040.000a) .0 0 0 CTN ON Cl4 •••n v ua r.4 4t
172
.. I i 0 Cl) a) L. 14 E 114Q)CL) 4 44 ç CL, li) 0 O CI 4., I DI 0_4 4... a+ Cl) O Or 4.10) 44 rI • ....I 4 CD 0 › • E 1:), - 0 '4) 0 (CE ro a) c .0 n:) o a) ou ...) a) 44 44 144 -4-1 Q..-QV 4 2 0 -IV Q) Q) 0 .,..1 0 +-I 0 ‘.4 O 0 C 44G) >1 cn ..• 14 ..-4 14 C • te) 44 = 4) 0a) 0 14 1-4 H 0 0 0 a) a) ra a •-, Q) 4.J (Ca) 0W a) .4 Q). a.) Q.) .., .0 14.4 4 V/ CO • 0.0 0V • V.0 V 4 0 0 .... O .4 01 W 4...n • 0 0 0 0 0 C U .-( 0 47 2 •.• 0 4..) Q) (CV04 4.1 0 4... 0 0 t'14 Q)0 4.• In ..) 0 ...)41..-1 ...4 4.) 0 01 4 r-1 -4 v.. 0 r•-• 0 U 0 >1 -, 44 4-1 4 0 V 14 H 4.4 al V 04 4 4-4 .4.00 .. . 1,, 4.., .....0 . g p 0 0 > 14 O Z o nz) 4 4.1 4) .-4 (CEOO 3 3.4 Cl-, 2 0, 2 4-'0, . _4 14 14-'o U ..4 •-• .0 14 ).., 0 0.) 0 A 00 00 gr, C.) 4 0 CO A 0 C.) 0 0 7-1 rad A k 4. +-I 0:4 .4 g 0 0
0) 0, 01 0, a) Co WO' .140 4-40 4.10 .440 •• 4-4 •n•4 •• .4•4 •• 4-4 44 4. .4-4 CI) 41 0 0 C.) 4.• Q.) 04.4 0 04-' 0 0.4.4 O 0 0 0 4.1 .4 0 0 4..) .-i al 0 4.! ri 0 0 44 ri 0 O 0 0 0000 0=00 0000 0000 Z Z Z Z.000 Z.000 Z.000 Z 4 0 C.)
O 0 I 0 Z ..I -4 Ci) dP > > ee 44 dP dP de cle 0 cIP de _4 dP ..4 m 0 m 0 0 in m o cy .4 In ,-. .4 ci) c.4 In c0 u) h 0 h 0 V Z 1 i O I C 4.) i I I I . n . I . O I-4 ..... 0 -Q) 0 .4 0 •14 0.1 a) a) w n. 44 a) n...... , 0) 4) .14 44 •• (I) 44 .‘J 44 44 ..--- ...1 44 •-••• ••••1 4 4 .4 4-1 ...4 4) C .. .. • .4 • v. C.) -.I U .4 C.) 4/) 0 .6) 0 40 Cil U 0 C.1 co ...• r-4 co 4..• n-•4 Cl) r-1 O I-1 44 () r-1 1-1 4 4 r4 4) r-4 CO la .--1 0 0 r-4 40 a) C) 0 W 0 cl) 0 Cl.) -40 0 -.0 0 0 44 •-• 0.) t.i 44 IN 144 4 .... 4 %•-• O dP 0 4-4 dP dP .. . C.) . 0- . c..)VdP cc-) V U .2 dP ul T1 .0 dP M 0 V dP 0 V) tIP 0 a) dP 0 0 V dP a) ONOO 0 ev 0 0 its .4 ..• 0 c0 ...) OC 44 Oat' 44 0 01 4) in 0 .4 N 14 0 CO C•4 44 0 4-4 +4 0:1 el W 4•1 0 r..1 Cll +-I IC CV 4-1 0) 44 1 1 4.1 4-1 V 4) V 44 44 1 a) 44 0 I 0.) WI W a.) i CLI CU I 0 Cl/ 0) I G CI) 0 I 11 CI) 4.., ...4 0) 0 44 44 a) 0 4-• 0 44 a) 0 44 CI) 0 4,-.., ,4 g. N 4, 4-1 4) O N 4.) 44 .41 ea 44 0% ....1 N th ..-I N ...4 0, ....1 N .44 ID, 0 .4 •-4 44 a) C) 4.1 4444 0-4 r-1 4, .1-1 .-4 4., 0 .--.14 .1 2 1-110 4) 2 o2 -4 .1,-, 0 I.40o0a) -10o o 1.1 0 E 0 1.4 W 0 14 W g, o 14 a 0 I 0 >I 0 1.1 IC I 01 >4 >1 00 0 ›. I01 >, 0 CO G /4 4 0 0 G 14 4 0/ /71 14 = P 0) IT $4 g g• '6,1 ,14 g OA' g 0, .0° gip g Er .8 g) g OP :f4e
• • . 8 • • • 44 44 4-4 44 4.4 H 44 140 140 140 140 140 140 140 (Ca) 0 40 0 0 (Ca) (Ca) (CE (Ca) I .-i g I ,--i g, I I-. 00 I 4-4 g, (.44 0g I.- 0 1 .41 Er W OO'0 a) z w 0 0 p 0 0 WOO' 0 Z O 01 rt:1 0 01 0 0 tim 0 0 an 2) 0 Dr 40 47; G CC/ 0 -40 ..-4 0 - 4 0 ....i0 44 oe0 . 41 .1 .. 4:: 1. . 4. .4 n 44 ga ... ,.1.4 x0 . O '0 V V V V V V O 0 0 0 0 0 0 0 0 0 0 0 0 0 X 44 • V .a...) • V .., • V 44 • •(:) 4) • V 44 • V 44 • V VO VO VO VO VO VO VO Q) Q)0= CI) CV = Cl/ 0) 0 Q) W00 C11 0.1 0 a)0 0 C1) al 0 En 0 0 40 0 0 Ii) 0 0 V) 0 0 (I) 0 0 0 0 0 0 G 0 14-.4 141-I S4 4.1 H 14-414H 14 +4 H 14-.4141.4 14 4-1 H 14.414H 0 0 'Ca) (Ca) iti 0 'Ca) (Ca) 'Ca) O $4 0 0140 0 /4 0 0140 0 14 0 0140 0 H 0 C.) IT 44 L) Q444) C.) CT A-. L) Q'44-4 U CT 4-• L) O'444)
V'0 '0 al a) '18 a) a) a) 44 44 -4, 44 44 .14 ta MI (C) (C) tC1 0 tn r.), V, tr, O V V 0 0 0 44 4-1 44 .4-1 44 4 4 14 14 H H H H O 0 0 0 40 0 › › › › › ›
O 0 a) 0 a) 0 0 X X X X X X .X U U U U U C.) c.) (0 0 0 0 0 0 co X X X X X X s I I I I i I I Cl, 0 a) a) a) a) w a) 14 14 14 H H H tr ,c) 0,0 0,0 01 0 0,0 0,0 .E"E .0 0 g 2 0a) g 2 0 0 1 2 1 g g 2 CO U) (0 (1) 0)11) (0 (1) ca ta COU) COQ)
>4 IF.1 . -0 0 0 cc Ln 14 0 0 0 ri es, rt) In Q. s a) .4 o(1) Q. .4 to APPENDIX B
SCATTERGRAMS
173 174
5.0 -
4.0
30
2.0
o 0 1.0
(f)
0.0 0 160 260 300 Calcium Conc. (mg/I)
Figure B-1. Scattergram of strontium versus calcium
5.0-
40
2,0
• • 0 1.0 • • • • •• • • • t • • • • 0.0 0 110 115 210 Magnesium Conc. (mg/I)
Figure B-2. Scattergram of strontium versus magnesium 175
5 0 -
4.0
3 0
2.0
• 1.0
• • • • • • • • • • 0.0 • o 160 200 300 400 500 Sodium Conc. (mg/I)
Figure B-3. Scattergram of strontium versus sodium
5.0 -
• 4.0 cy)
3.0
0
2.0 ci ci 0 L. 1.0
U.) • • • I • • • • • 0.0 • • 1 0 2 4 6 6 lo Potassium Conc. (mg/I)
Figure B-4. Scattergram of strontium versus potassium 176
5.0 -
4.0
3.0
2.0
• •
1.0 • • 0.0 • •• • 0 260 460 660 800 Sulfate Conc. (mg/I)
Figure B-5. Scattergram of strontium versus sulfate
5.0-
3.0 - o L)
2.0
o 1.0 • I . • • ••• • 0.0 0 5 10 100 150 260 250 36 0 350
Figure B-6. Scattergram of strontium versus chloride 177
5.0 -
czn 4.0 -
(2; • 3.0
0 C)
2.0 - D
0 1.0 - +4,
Cf-) • • • . . • • • • % • 0.0 , O 160 260 • 300 Bicarbonate Conc. (mg/I)
Figure B-7. Scattergram of strontium versus bicarbonate
5.0 -
4.0
3.0
0.0 0 I ' ' 4 Carbonate Conc. (mg/I)
Figure B-8. Scattergram of strontium versus carbonate 178
5.0-
4.0
3.0
2.0
1.0
• 0.0 0 4 10 12 Fluoride Conc. (mg/I)
Figure B-9. Scattergram of strontium versus fluoride
5.0-
4 0 - CD •
3.0 -
2.0 -
• •
1.0-
0.0 0 lb 210 310 40 Silica Conc. (mg/I)
Figure B-10. Scattergram of strontium versus silica 179
5.0 -
4.0 CT)
3.0
0
2.0
• • •
rTh s_ 1.0 • • cr)
• • •• • • • 0.0 500 1000 1500 2000 Total Dissolved Solids (mg/I)
Figure B-11. Scattergram of strontium versus total dissolved solids APPENDIX C
PROCEDURES FOR THE CHEMICAL ANALYSIS OF STRONTIUM, CALCIUM, AND SULFATE IN ROCK SAMPLES AND WELL CUTTINGS
Samples of potential strontium source rocks obtained from field
work in the mountains surrounding the Ranegras Plain were analyzed for
total strontium by x-ray fluorescence. The acid extractable fraction of
these samples was analyzed for strontium and calcium by atomic absorp-
tion (AA) spectroscopy. The acid-extractable fractions of well cuttings
from two boreholes in the Ranegras Plain basin were analyzed for stron-
tium and calcium by atomic absorption and for sulfate by a turbidimetric
procedure.
Sample Preparation
Samples of the andesite, basalt, and silicified limestone were
broken into large chips with a rock hammer and then ground into a powder
with a rotary grinder. The caliche sample and gypsum samples from the
Granite Wash and Plomosa Mountains were ground with a mortar and pestle.
Well cutting samples for two wells, Well No. 7 [B(3-15)2dab,
Lab. No. 2621] and Well No. 64 [B(7-17)15dcd, Lab. No. 64] were obtained
in vials, one for each 20 foot interval, from the Arizona Department of
Mines and Geology. Due to the large number of samples from each borehole, composite samples from various depth intervals (Table 11) were prepared. The depth intervals ranged from 20 feet to 100 feet. The
180 181 selection of depth intervals was based on initial acid-soluble strontium analyses of 200 foot intervals and on the occurrence of gypsum. Gypsum correlated positively with elevated strontium concentrations; therefore, smaller depth intervals were analyzed in the gypsiferous intervals. For each depth interval, an equal mass of representative well cuttings (1-3 gram) from each vial was weighed into beaker. Each composite sample was then broken apart into individual sediment grains with a mortar and pestle. Individual samples of gypsum, if present, from each sample vial were analyzed separately.
Acid-Extractable Fraction Analysis
Approximately 1 to 2 grams (g) of powdered rock or ground-up well cutting sample was weighed to the nearest 0.1 milligram (mg) into a tared 100 milliliter (ml) beaker. Approximately 20 ml distilled water was added to each beaker. Dilute (5%) hydrochloric acid was added until gas evolution due to carbonate dissolution was not visible. The sample was stirred with a magnetic stirring bar and glass rod. The mixture was then adjusted to pH 6 with the dilute HC1. The samples were leached for seven days. Each day the pH was readjusted to pH 6 with the dilute HC1.
The liquid and remaining sample residue for each sample was filtered through tared Whatman No. 41 filter paper into 100 or 250 ml volumetric flasks. The sample beaker, filter paper, and sample residue was washed with dilute (pH 6) HC1 and distilled water, and the rinses were added into the volumetric flask.
The filter paper and residue was dried for three hours at 120°C and weighed to the nearest 0.1 mg. The percent insoluble residue was 182 calculated as the ratio of the weight of the dried residue to the orig-
inal sample weight. Magnetite present in the drill cuttings from the
first four depth samples from Well No. 7 adhered to the magnetic stir- ring bar and prevented accurate weighing of the residue for these
samples.
The gypsum samples from the Granite Wash and Plomosa Mountains
and from well cutting samples were dissolved directly into 100 or 250 ml
distilled water adjusted to pH 6 with HC1 (Table 11). The sample size
for the gypsum samples was 100 to 200 mg. This mass was calculated to be well below the solubility of gypsum. A small amount of turbidity was visible after dissolution of the samples, but was too small to be
detected as a residue on the filter paper after filtration.
Calcium and Strontium Analysis by Atomic Absorption
Lanthanum chloride-potassium chloride solution was added to each
extract sample in the ratio of 1 ml of LaC1 3 -KC1 to each 10 ml of sample
solution. The samples were then diluted to volume with distilled water.
The addition of 1 percent lanthanum to the samples and standards con-
trols chemical interference from silica, aluminum, and phosphorus during
analysis of calcium and strontium by atomic absorption. The potassium
is added to decrease the ionization of calcium and strontium in the
flame (Fishman and Downs, 1966). The LaC1 3 -KC1 solution was prepared by
dissolving 117.3 g La2 0 3 in a minimum amount of dilute HC1. Then 19.1 g
KC1 was added and the solution was diluted to 1000 ml with distilled water. 183
The sample solutions were aspirated directly with a Perkin-Elmer
Model 306 atomic absorption spectrometer using the standard operating conditions recommended by the manufacturer (Perkin-Elmer, 1976) and listed in Table C-1. Due to the potential interferences in the analysis of calcium and strontium, the samples were analyzed by two methods:
(1) direct analysis of the acid extract and (2) the method of known additions. The calcium and strontium concentrations calculated by the two methods agreed within 3 to 29 percent (Table 9).
Aqueous strontium standards at concentrations of 1, 2, 3, 5, and
10 mg/1 were prepared by dilution of a 100 mg/1 strontium standard
solution. This stock solution was prepared by dissolving 0.1684 g of oven-dried SrCO 3 in a minimum amount of dilute HC1, and then diluting to
1 liter.
Calcium standards of 1, 2, 3, 5, and 10 mg/1 were prepared by
the dilution of a commercially available 1000 mg/1 calcium standard with pH 6 HC1.
Both the strontium and calcium standards were spiked with 10 percent (v/v) of the LaC1 3 -KC1 solution prior to the final dilution.
Sulfate Analysis
A turbidimetric method, Standard Method 426C (APHA, AWWA, WPCF,
1985) was used to analyze aqueous sulfate. The sample size of the acid
extract was 10 ml. The absorbance of the precipitated barium sulfate at
420 nanometers was then immediately measured using a spectrophotometer.
The absorbance was converted to mg/1 sulfate using the absorbance of 184
Table C-1. Operating conditions for atomic absorption spectrophoto- metric analysis of calcium and strontium.
Operating Conditions for Atomic Absorption Calcium Strontium Spectrophotometer
Wavelength (run.) 422.7 460.7
Slit Setting (nm.) 0.7 0.7 Light Source Ca-Al-Mg combination Strontium hollow Hollow cathode lamp cathode lamp Flame Type Air-acetylene; Air-acetylene; oxidizing, lean, blue slightly reducing, bluish-yellow
Burner Head 2-inch burner head, 2-inch burner head, flame parallel flame parallel Linear Working Range 0-5 ppm, 0-5 ppm, curve-corrected curve-corrected to 10 ppm to 10 ppm 185 standard sulfate solutions of 1, 5, 10, 20, and 50 mg/l. Sample dilutions were made when required.
Strontium and Calcium Analysis by X-Ray Fluorescence Analysis
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