NORMAN C. WARDLAW Department of Geological Sciences, University of Saskatchewan, Saskatoon, Canada
Carnallite-Sylvite Relationships in the
Middle Devonian Prairie Evaporite
Formation, Saskatchewan
Abstract: Abrupt lateral and vertical changes from red carnallitite (carnallite-halite rock) to red sylvinite (sylvite-halite rock) occur in the Prairie Evaporite Formation between Watrous and Kandahar, Saskatchewan. Such changes are of considerable economic importance, since carnallite has undesirable physical properties and a relatively low content of potassium. The following four types of relationship between sylvinite and carnallitite are considered: (1) the rocks are facies equivalents deposited in different areas from essentially contemporaneous brines; (2) carnallite formed by reaction of sylvite with magnesium chloride brines; (3) sylvite derived from carnallite by leaching of magnesium chloride; (4) sylvite, as presently found, not directly related to carnallite, but formed through solution of pre-existing sylvite with subsequent crystallization. Sylvinite overlies carnallitite, the reverse of a normal depositional sequence. The distribution of traces of bromide and rubidium in the chloride minerals indicates that red sylvinite was formed by leaching of magnesium chloride from carnallitite. This conclusion is substantiated by textural observations at carnallite-sylvite contacts, where red sylvite has re- placed carnallite and inherited iron-oxide inclusions from carnallite. A comparison of the proportions of carnallite and sylvite, in a given potash zone, from a region of carnallitite to an adjacent region of sylvinite, reveals that the amount of sylvite present cor- responds to the amount which could be derived from carnallite by leaching of magnesium chloride. The potash zones are cumulatively about 50 ft thicker where they are red carnallitite than where they are red sylvinite. Since the total thickness of salts can be determined by seismic techniques, this provides a valuable prospecting guide to the presence of local areas of carnallitite. Not all the sylvite present is derived from red carnallite. A clear variety of sylvite, termed "clear sylvite," can be distinguished from red sylvite by the absence of iron-oxide inclusions and by a relatively small rubidium content (0.003 weight percent). Petrographic evidence indicates that red carnallite locally has replaced clear sylvite. Seventeen potassium-argon dates on red sylvite range from Permian to Mississippian; two samples gave younger ages. These are minimum ages and the alterations of carnallite to sylvite may have been essentially contemporaneous with deposition.
CONTENTS Introduction 1274 Geochemistry 1282 Acknowledgments 1274 Methods of analysis for bromide and rubidium 1282 Reference core 1275 Generalizations from trace-element profiles . 1284 Clear sylvinite 1275 Generalizations from trace-element profiles in Red carnallitite 1275 relation to experimental data 1284 Red sylvinite 1275 Experimentally determined partition coef- Stratigraphy 1275 ficients for bromide and rubidium . . . 1286 Mineralogy and petrology 1278 System NaCl-KCl-MgCU-HaO 1287 Proportions of major mineral constituents . . 1278 Bromide and rubidium in sylvite derived from Iron oxide inclusions 1278 carnallite 1288 Grain relationships 1279 Relationship of red sylvite to carnallite . . . 1289 Structures 1280 Potassium-argon dating 1290 Insolubles 1282 Conclusions 1291
Geological Society of America Bulletin, v. 79, p. 1273-1294, 9 figs., 3 pis., October 1968 1273
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References cited 1293 2. Photomicrographs of sylvite and carnallite. 1 „, 3. Photomicrographs of halite, svlvite, and car- \ „ .e Figure nallite .jSectlon 1. Area of study and extent of Prairie Evaporite 1274 2. Representative rock types from reference core 1276 Table 3. Vertical and lateral transitions from carnallite 1. Comparison of units weight of carnallite and to sylvite 1277 sylvite in potash zone 2 1278 4. Fabric diagrams for goethite and hematite in 2. 29 values for goethite and hematite .... 1279 carnallite 1280 3. Distribution of insolubles in the upper part of 5. Rock types from potash zones 1281 the Prairie Evaporite 1283 6. Structures in Prairie Evaporite salts .... 1285 4. Bromide and rubidium in halite, sylvite, and 7. Trace element distribution in salts of ideal carnallite of Prairie Evaporite Insert profile 1288 5. Experimentally determined bromide ratios and 8. The system NaijClj-KjCU-MgCls-HzO ... 1288 those for Prairie Evaporite 1286 9. Curves for bromide and rubidium in sylvite 6. Weight percentages of bromide and rubidium derived from carnallite 1289 in halite, sylvite, and carnallite .... 1287 7. Bromide and rubidium in sylvite derived from Plate carnallite 1290 1. Mineralogical and geochemical profiles . . . Insert 8. Potassium-argon dates 1291
INTRODUCTION of sylvite with magnesium chloride brines; (3) sylvite derived from carnallite by leaching of The subject of this study is the potash-bear- magnesium chloride; (4) sylvite, as presently ing upper portion of the Middle Devonian found, is not directly related to carnallite, but Prairie Evaporite Formation in the region be- formed through solution of pre-existing sylvite tween Watrous and Kandahar, Saskatchewan with subsequent crystallization. (Fig. 1). The 15 available cores reveal abrupt Mineralogical, petrographic, geochemical, lateral and vertical changes from carnallitite and stratigraphic data are used to define the (carnallite-halite rock) to sylvinite (sylvite- relationships between sylvite and carnallite and halite rock). One of the major objectives is to to deduce how the potash zones developed to define the relationship between sylvinite and their present form. carnallitite and to explain the vertical and lateral transitions from one to the other. Such ACKNOWLEDGMENTS transitions are of considerable economic im- Grants in aid of research from the National portance, since carnallite is to be avoided in Research Council, Canada, and the Saskatche- potash mining because of its relatively low wan Research Council are gratefully acknowl- potassium content and undesirable physical edged. The Geological Survey of Canada properties. provided funds for the radiometric age deter- The following four types of relationship are minations. The writer takes pleasure in thank- possible between sylvinite and carnallitite: (1) ing Messrs. H. and K. Haugen and Mr. G. the rocks are facies equivalents deposited in Lawrenz for their assistance in making bromide different areas from essentially contempora- analyses, Mr. W. Ross of the Saskatchewan neous brines; (2) carnallite formed by reaction Research Council for the analyses on car-
;3W2 ROE22W2 RGE2IW2 ROE20W2 RGE I9W2
SCALE IN MILES Figure 1. Area of study and extent of Prairie Evaporite in Saskatchewan (inset).
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bonates, and Profs. R. E. Folinsbee and H. The penetration of carnallite along halite and Baadsgaard for undertaking the radiometric sylvite cleavage planes and grain boundaries, age determinations. The staff of the Saskatche- together with the occurrence of carnallite rims wan Government Core Laboratories in Regina, on sylvite, suggests that carnallite is re- in particular Mr. G. F. Runtz, cheerfully placing halite and clear sylvite. provided their services for core examination and the collection of samples for analysis. Mr. Red Carnallitite E. Hawkins prepared the thin sections and Mr. Zone 2, of the Kutawagan core, is composed W. McMillan assisted with drafting. mainly of red-brown-colored carnallite with Special acknowledgment is made to Mr. subsidiary clear and milky crystals of halite, D. W. Hurd of the Southwest Potash Cor- but traces of clear sylvite also occur. The red poration who co-operated enthusiastically and color of carnallite results from iron oxide in- made many valuable suggestions. clusions. Where clear halite is locally abundant, The writer is grateful to J. B. Droste for grain boundaries between carnallite and clear confirming identifications from diffraction halite are commonly amoeboid, and carnallite diagrams. extends along halite cleavages and along halite- Finally, thanks are due to Drs. W. T. halite grain boundaries. Where carnallite is Holser, M. S. King, R. Kiihn, and W. O. dominant, halite grains are mainly euhedral Kupsch for critically reading the manuscript and of the milky variety. This rock type is and for their various comments. called red Carnallitite (Fig. 2). Grain relation- ships suggest that carnallite has replaced REFERENCE CORE crystals of clear halite, but not of milky halite. Kutawagan 6-29-30-21W2 has been chosen as a reference core for the area. In the upper Red Sylvinite 250 ft of the Prairie Evaporite, three major Zone 3, in the Kutawagan core, is composed zones of potassium-bearing salts (potash zones) mainly of red sylvinite. The halite is clear, with are recognized and are numbered in deposi- irregular, greenish masses of insolubles pref- tional sequence after Goudie (1957, p. 10), erentially on the lower sides of clusters of with the refinement that Goudie's zone 3 has halite grains (Fig. 2). Sylvite grains are red- been divided into a lower and an upper unit, brown, the red coloration being restricted to 3A and 3B (PI. 1). the margins of grains where iron oxide in- The potash zones are interlayered with units clusions are abundant. Where red sylvite is in of halite. Minor laminae of anhydrite, car- contact with red carnallite, the sylvite is seen bonate, and clay are common. The Second to have replaced the carnallite and to have in- Red Beds, which are composed of red and herited iron-oxide inclusions from carnallite. green dolomitic, anhydritic mudstones, overlie Thus, red carnallite is older than red sylvite, the Prairie Evaporite Formation. but younger than clear sylvite. Insolubles are defined as components not Clear sylvite, although most characteristic of readily soluble in water, but which exclude zone 1 in the Watrous-Kandahar area, also iron-oxide inclusions in the potassium minerals. occurs in small proportions in zones 2 and 3, The rock types described below occur in the particularly near the bases of these zones. Red other cores examined but are not restricted to Carnallitite and red sylvinite are both common the particular zones of their occurrence in the rock types in zones 2 and 3, but have not been Kutawagan core. observed in zone 1. Primary chevron halite crystals of the type Clear Sylvinite described by Wardlaw and Schwerdtner (1966, Zone 1 consists of large, transparent-to- p. 331) are not observed anywhere in the milky grains of halite with smaller, transparent- potash zones or associated halite units. Chevron to-yellow-brown grains of sylvite. Sylvite grains are restricted to halite in the lower grains, amoeboid in shape, are without con- portion of the Prairie Evaporite. spicuous inclusions but commonly are encased by carnallite. Extensions of carnallite lie along STRATIGRAPHY halite and sylvite cleavage planes and halite- The potash zones are remarkably continuous sylvite grain boundaries. Insolubles occur laterally and can be traced throughout the mainly along grain boundaries between halite area (PI. 1). In potash zones 2 and 3, abrupt grains. This rock type is called "clear sylvinite" vertical and lateral changes from red Carnal- (Fig. 2). Carnallite is recorded where it occurs. litite to red sylvinite can be noted. Cores 16-10
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CLEAR SYLVINITE WITH CARNALLITE
Figure 2. Representative rock types from reference core (Kutawagan 6-29-30-21W2). Plate 1 details mineral distribution in core. Halite (white), sylvite (coarse stipple), carnallite (fine stipple), insolubles (black).
and 4-29, of Figure 3, illustrate changes in area, toward the basin margin, carnallite ap- vertical sequence from red carnallite to red pears to increase, and sylvite to decrease in sylvite within a zone. Cores 5-14 and 4-16, abundance (M. Holter, 1967, oral commun.). about two miles apart, illustrate lateral change This, too, is the reverse of a normal depositional from red carnallitite to red sylvinite within situation in which a concentration of the more zones 2 and 3A. Individual zones are thinner in soluble carnallite would be expected toward the regions of sylvinite than in regions of carnal- basin center (a regressive shoreline accompany- litite. The total potash section is about 50 ft ing volume reduction by evaporation). thinner where all zones are sylvinite. Interven- Structural lows on the top of the Prairie ing halite units are of more uniform thickness. Evaporite correspond to regions of sylvinite. Figure 3 illustrates that sylvite overlies This cannot be explained entirely by the carnallite, both in the section as a whole and thinning associated with lateral change from within individual zones. This is the reverse of carnallitite to sylvinite. In the region of town- the normal sequence produced during progres- ship 31, ranges 24 and 25, the top of the sive evaporation of magnesium-sulfate-de- Prairie Evaporite is locally 125 ft low, but only ficient sea water, where carnallite overlies 50 are accountable to the lateral change from sylvite (Braitsch, 1962, p. 76). carnallitite to sylvinite. Such lows may be To the north of the Watrous-Kandahar due to local solution at the base of the Prairie
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Evaporite salt, with consequent collapse, or the area, in township 29, range 24 (Bishop, due to faulting independent of solution. These 1954, p. 480), with total removal of the alternatives can be distinguished only with Prairie Evaporite and collapse of overlying additional information on the elevation of the formations. lower contact of the Prairie Evaporite and the As already noted by Hurd and Shaw (1966, underlying formations. Such information is not p. 44), there is a relationship between the total available. However, solution collapse ap- thickness of the Prairie Evaporite and the parently has occurred in the southern part of presence of carnallite, the formation being
3B
3A
ZONES OF POTASSIUM MINERALIZATION I,2,3A,3B. ZONE BOUNDARIES. BOUNDARY SEPARATING SYLVITE ABOVE FROM CARNALLITE BELOW. lll!llll!!l!llll pT|= 100 % KCI cnsu
[£1=100% KCI MgClj6HtO MM
MINERALOGICAL DATA FOR 4-29 INFERRED FROM GAMMA-RAY AND NEUTRON LOGS. 0 50 100 FEET VERTICAL SCALE I I I Figure 3. Vertical and lateral transitions from carnallite to sylvite. Percentages of carnallite and sylvite are plotted, the balance to 100 percent being halite and insolubles. For core locations, see Figure 1.
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thicker where there is carnallite. Since the TABLE 1. COMPARISON OF UNITS WEIGHT OF total thickness of the Prairie Evaporite salts CARNALLITE AND SYLVITE IN POTASH ZONE 2* can be determined by seismic surveys, such surveys are of great importance in delimiting Carnallitite (average thickness 50ft) local areas of carnallitite. Carnallitite bodies are Constituent Insolubles Halite Sylvite Carnallite notably irregular in shape and in size, and it would be impractical to delimit them by Average weight percent 3.5 40.2 1.5 54.8 drilling. For the seismic method of prospecting Average absolute to be effective, it is necessary to distinguish units weight 3.2 37.3 1.4 50.5 regions in which the total Prairie Evaporite is thinner than regional due to lateral change Sylvinite (average thickness 32 ft) from carnallitite to sylvinite, from those in Average weight which it is thinner for other reasons. This can percent 4.0 70.8 21.7 3.5 be accomplished with regional information on Average absolute salt thicknesses and elevations for the contacts units weight 2.6 46.5 14.2 2.3 of formations overlying and underlying the Core used in compiling the above data: Prairie Evaporite. Such information, for the carnallitite, 5-14-31-24W2, 5-15-30-23W2, 16-10-30- area of study, is presently confidential. 22W2, 1-27-31-16W2 Stratification in the upper part of two Sylvinite, 1-13-32-20W2, 15-33-31-24W2, 4-10-32- Prairie Evaporite cores is inclined, indicating 24W2,8-36-31-25W2,12-22-30-25W2,4-16-31-24W2, post-depositional movement. In 4-20-31- 4-20-31-24W2 24W2 the dip increases downward from 11 degrees to 22 degrees, through 175 ft of * Average absolute units weight are calculated on the section; in 5-14-31-24W2, dips decrease basis of a constant cross-sectional area. Based on chemical downward from 15 degrees to 5 degrees, analyses available from Saskatchewan Government files. through 185 ft of section. MINERALOGY AND PETROLOGY Iron Oxide Inclusions Proportions of Major Mineral Constituents Carnallite and sylvite are colored red by A comparison can be made between the inclusions of hematite and of a fibrous mineral proportions of carnallite and sylvite in a given which has been identified tentatively as potash zone. In this case zone 2 has been goethite (a — FeO-OH). Goethite fibers are selected, where the zone is dominantly carnal- about lju in diameter and from 100 to 200jt long litite, and where it is dominantly sylvinite. (Pi. 2, fig. 1). These fibers previously were Wells close to each other were chosen. misidentified as koenenite (Wardlaw and Where zone 2 is carnallitite, there is an Schwerdtner, 1963, p. 76). A sample of in- average of 50.5 units weight of carnallite, which clusions was dissolved out of carnallite, with can be compared with 14.2 units weight of water, and 26 values were read from a Guinier sylvite, where zone 2 is sylvinite. photograph (Table 2). Using the molecular weights of carnallite and All 26 values are accountable to goethite and sylvite, it can be calculated that 50.5 units hematite, within 0.13 degrees 2d, with the weight of carnallite contain 13.6 units weight exception of the lines at 36.62 and 62.5 de- of potassium chloride. Thus, from Table 1, grees. the absolute amount of potassium chloride is The orientation of hematite plates and approximately constant in zone 2 from regions goethite fibers in carnallite was measured with of carnallitite to regions of sylvinite. The a universal stage. The maximum difference magnesium and sodium chloride contents of the between the real and apparent inclination of zone change laterally, but not the potassium fibers is approximately 2 degrees. The orienta- chloride content. It may be noted that the tions of more than 100 fibers, in each of six absolute weight of halite is greater where zone random grains, were measured and a preferred 2 is sylvinite than where it is carnallitite. orientation of the fibers in carnallite is ap- Although the percentage of insolubles is parent. The long axes of fibers are preferentially greater in zone 2 where the zone is sylvinite, arranged parallel to [100] and to [110] and the absolute amount of insolubles is slightly [110] (Fig. 4). Using cell dimensions for less. carnallite after Braitsch (1962, p. 10)
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a0 = 9.56 A bo = 16.05 A c0 = 22.56 A sylvite grains have orientation and density of occurrence similar to those of inclusions in adjacent carnallite grains (PI. 2, figs. 3 and 4, and PI. 3, fig. 1). [100] A [110] = 59° 13' The goethite fibers in sylvite are much [010] A [110] = 30° 47' shorter than those in carnallite, rarely exceed- ing 40/i in length. Very finely disseminated The preferred orientation and uniformity of iron, so small that individual particles are not distribution of fibers in carnallite grains suggest visible at 500 X magnification, also occur around either that fibers and carnallite crystallized the margins of sylvite grains. together, or that goethite formed during an Red staining also is noticeable at contacts unmixing process. It seems unlikely that between sylvite and greenish-colored insolubles goethite fibers pre-existed and were included in (PI. 3, fig. 2). No such staining occurs in halite carnallite. adjacent to insolubles. A similar relationship The orientation of poles to hematite plates between red sylvite and green clay was re- shows pole maxima along the carnallite c-axis; corded by Schaller and Henderson (1932, p. that is, hematite plates lie preferentially in 24). (001) of carnallite. Hematite (0001) coincident with carnallite Grain Relationships (001) is a relationship which has been recorded Red carnallite grains interpenetrate with by Johnsen (1909, p. 168), Spangenberg and adjacent red sylvite grains, processes of which Neuhaus (1930, p. 437), and Seifert (1937, p. extend along planes of inclusions and twin 185). planes in carnallite (PI. 2, fig. 5). Isolated Several workers have assumed that the portions of carnallite have common crystal- hematite in carnallite was formed by unmixing lographic orientations with larger adjacent and oxidation of ferrous iron from solid solution carnallite grains. Hematite and goethite in- in carnallite. Johnsen (znBraitsch, 1962, p. 172) clusions, distributed more or less uniformly in represented ferrous chloride in carnallite as carnallite, occur in abundance along carnallite- hydrolyzing to form hematite, 6(KC1 -FeClo- sylvite grain boundaries and color the outer 6H2O) ->• 4FeCl3 + Fe2O3 + 6KC1 + 3H2 portions of sylvite grains (PI. 2, fig. 5). These + 33H2O, followed by further reaction of iron relationships suggest that red sylvite is younger chloride with Mg(OH)2, 4FeCl3 + 6Mg(OH)2 than, and has replaced, carnallite, inheriting -- 2Fe2O3 + 6MgCl2 + 6H2O. hematite and goethite inclusions from carnal- An alternative to unmixing is that the lite. hematite and carnallite grew contemporane- Halite in red sylvinite is commonly euhedral ously. In either case, the epitaxy between to subhedral, while sylvite is anhedral. Green hematite and carnallite will not be fully ex- insolubles are associated with halite, around the plained until the crystal structure of carnallite margins of grains as well as within grains. is known with certainty (Fischer, 1959). Plate 3, figure 3, illustrates portions of car- Hematite and goethite inclusions color the nallite, with common orientation, isolated in sylvinites red. In contrast to the occurrence in halite. Elsewhere, amoeboid grains of halite are carnallite, fibers and plates in sylvinites are seen with rounded processes aligned with trains commonly without preferred orientation and of inclusion in carnallite (PI. 3, fig. 4). Such a occur around the margins of grains (PI. 2, relationship suggests that halite replaced figs. 2 and 5). Locally, however, adjacent to carnallite. massive carnallite, hematite inclusions in Plate 3, figure 5, illustrates a thin section of TABLE 2. 26 VALUES, FROM GUINIER PHOTOGRAPH, FOR SAMPLE AND FOR GOETHITE AND HEMATITE (COPPER Kaj RADIATION) * Sample 21.2224.1526.4533.1735.65(36.62)40.9 49.5 53.3 54.1557.5 (62.5) 64.0575.3585.0 Goethite 17.82 21.24 26.5 33.28 36.8 40.04 53.22 57.5 59.18 Hematite 24.16 33.28 35.74 40.98 49.48 54.22 62.72 64.18 * Values for goethite and hematite are from American Society for Testing and Materials Powder Diffraction File (1963).
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Figure 4. Fabric diagrams for two carnallite grains illustrating orientation of goethite fiber axes (circles) and poles to hematite plates (crosses) in relation to crystallographic axes of carnallite. Illustrates tendency of hematite poles to parallel c-axis of carnallite and tendency of goethite fibers to lie in (001) of carnallite, parallel to "a," and at about 60 degrees from "a" (which corresponds to [110]).
red sylvinite in which three portions of sylvite, red carnallite red sylvite having common orientation, are separated by red carnallite halite halite. Each of these portions contains only a red sylvite halite small boundary region of red rimming, sug- clear sylvite carnallite gesting that replacement of sylvite by halite halite carnallite has occurred subsequent to the formation of Structures red rims. Halite units interstratified with the potash In Figures 5B, 5C, and 5D, carnallite is seen zones commonly have vertical structures in ad- to occur preferentially along halite-halite grain dition to horizontal stratification. Beneath boundaries and in embayments in halite. Halite- sylvinite zones, vertical fingers of sylvite tran- carnallite grain boundaries are highly irregular sect halite units (Figs. 2 and 6B). Underlying and largely controlled by halite cleavages, sug- carnallitite zones there are vertically elongate gesting that the halite grains are resorption fingers of carnallite (Figs. 2 and 6F). Similar shapes. elongate masses of carnallite and sylvite occur Carnallite also occurs preferentially along in halites below the lowest potash zone, de- halite-sylvite grain boundaries, with embay- creasing in abundance down section. Carnallite ments in clear sylvite occupied by carnallite wedges selectively follow cleavage planes in (Figs. 5C, 5E, 5F, and 5G). Here, carnallite large halite crystals (Fig. 6H). Figure 6H also appears to be younger than clear sylvite and illustrates a geopetal structure; irregular replacing it marginally. These grain relation- pockets in halite contain insolubles, sylvite, ships may be summarized as follows: and carnallite in upward sequence.
A. Red sylvinite. Sylvite grains are anhedral with red rims containing hematite and goethite inclusions. Halite grains are larger, occur in clusters, and have associated irregular patches of insolubles. From 4-10- 32-24W2 at 3392 ft. B, C, and D. Red carnallitite. Carnallite occupies large embayments in halite and occurs preferentially along halite-halite grain boundaries and halite cleavage planes. B, C, and D are from 1-27-31-16W2 at 3350 ft, 1-27-31-16W2 at 3359 ft, and 5-14-31-24W2 at 3506 ft, respectively. E, F, and G. Clear sylvinite with carnallite. Sylvite grains clear to yellowish and without red rims. Com- monly enveloped in red carnallite which occurs preferentially along halite-sylvite grain boundaries, halite cleavages, and as embayments in sylvite. E, F, and G are from 5-15-30-23W2 at 3601 ft, 6-29-30-21W2 at 3661 ft, and 1-13-32-20W2 at 3336 ft, respectively.
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O 5 IP cm. Figure 5. Rock types from potash zones. Halite (white), sylvite (coarse stipple), carnallite (fine stipple), and insolubles (black). (See descriptions on facing page.)
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Local pockets of sylvite and carnallite occur exposed Devonian, Silurian, and Ordovician immediately above, but not below, prominent carbonates and shaly carbonates. laminae of insolubles in the interzone halite The insolubles in the potash zones are of units (Figs. 6A, and 6C). These occurrences, green color and are commonly associated with combined with the observation that sylvite clusters of halite crystals (Fig. 5A). In the up- and carnallite occur in vertically elongate permost halite unit and in the lower portion of masses cutting through halite, suggest that the Second Red Bed, the insolubles are both magnesium and potassium chloride brines green and brown colored. moved down through the halite units and were Where insolubles occur as distinct laminae, trapped locally above layers of insolubles. rather than in intergranular positions, the In cores 4-20-31-24W2 and 5-14-31-24W2, upper contacts tend to be sharp and the lower stratification is inclined at angles of up to 22 contacts diffuse. Laminae of insolubles are degrees to the core axes. Trains of insolubles common at the upper contacts of potash zones. are arranged perpendicular to stratification and In the larger masses of insolubles, fractures not to the vertical (Fig. 6G). Presumably the filled with red carnallite and halite are common trains of insolubles were emplaced prior to the (Figs. 6D, 6E). movements which caused tilting. GEOCHEMISTRY Insolubles The term "insolubles" includes all com- Methods of Analysis for Bromide and Rubidium ponents not readily soluble in water, with the The method of analysis for bromide is that of exception of iron oxide minerals within sylvite Van der Meulen described by D'Ans and and carnallite grains. Insolubles in the lower Hofer (1934) (see Schwerdtner, 1963, for portion of the Prairie Evaporite Formation English summary). The method as used is consist largely of anhydrite, with minor sensitive to about +0.0005 weight percent amounts of dolomite. Those in and above the bromide, the sensitivity depending on the potash zones contain anhydrite and dolomite, amount of sample used. Analytical errors are but also contain significant amounts of clay. insufficient to affect the trends described. X-ray diffraction of four samples from zone 3 X-ray fluorescence was used for the deter- revealed illite and chlorite as the dominant clay mination of rubidium. Since the bromine K«i minerals. Quartz, dolomite, and anhydrite also line interferes with the rubidium K/3i line, are present. bromine must be removed from samples con- The distribution of carbonates is shown on taining both bromine and rubidium before a Table 3. Calcite and dolomite were determined reliable determination of rubidium can be quantitatively by the gasometric method made. Bromine was removed by a method described in Dreimanis (1962, p. 520), and the devised by O'Donnell (1966, p. 102). To 10 error of the results, which are expressed as mis of solution near saturation with bromine- percentages of carbonates from the total sample bearing sample, 5 mis of 1/5 N KIOs and 2 analyzed, does not exceed +2 percent. Car- mis of 2N HNOj were added. The bromide was bonates vary from 3 to 60 percent by weight oxidized to free bromine, which was then of total insolubles, dolomite being the dominant eliminated by boiling to near-dryness. The carbonate. Total carbonates increase as a con- samples were taken up to 10 mis with water, stituent of the insolubles from potash zone 1 to at which point no bromide could be detected zone 3B (Table 3). by the Van der Meulen method. All standards Table 3 also shows that insolubles increase in and samples were treated in this manner. abundance upward in section from zones 1 to Runs on sylvite and carnallite standard 3B. Potash zones contain more insolubles than solutions indicated that the limit of detect- associated interbedded halite units, with the ability was 0.001 weight percent rubidium in exception of the uppermost halite unit, in carnallite or sylvite. Multiple runs on several which insolubles increase irregularly up to the sets of standards, with rubidium in the range overlying Second Red Bed. 0.0001 to 0.05 weight percent, produced The insolubles are similar mineralogically to variations of +0.001 weight percent. the Second Red Beds, and probably have Similar methods have been used by German similar origins. Clay minerals and carbonates workers in deducing the origin of Zechstein probably were reworked from adjacent areas of potash salts (Kiihn, 1955, p. 3; 1963, p. 107).
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Percent / Calcite percent in insolubles \ Percent Insolubles Carbonate in 1 Dolomite percent in insolubles ] Insolubles \Total Carbonate percent in insolubles/ ;>
Potash zone 2 4.0 2.2 3.1 2.4 4 4 6 2 6 2.9 7.5 5.0 33.2 7.9 40.7 Halitite unit / ////////
Potash zone 1 1.4 //////// 1.2 3.0 9.4 0 10.6 3.0 * Data on insolubles from Saskatchewan Government files. Percentages of insolubles are averaged for the units and zones listed. Blanks indicate that no analyses are available. L0M0
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Generalizations from Trace-Element Profiles halite, sylvite, and carnallite, for the static evaporation of present-day sea water which is (See PI. 1 and Table 2) magnesium sulfate deficient, at 25° C, are 1 to (1) Weight percent bromide in the halite of a 10 to 7 (Braitsch, 1962, p. 106-107). Para- halite zone is approximately the same as that of genetic, as used here, means contemporaneous halite in interlayered sylvinites and carnal- crystallization from the same brine. Ratios for litites. salts in the Prairie Evaporite are documented (2) In profile, the trends for rubidium in for comparison (Table 5). carnallite and sylvite are the reverse of those The validity of comparing the absolute for bromide. That is, rubidium increases up- amounts of bromide in Devonian salts (observa- ward in the profile whereas bromide decreases tion 5, below) with bromide in salts from and vice versa. present-day sea water depends on the as- (3) Bromide in halite and sylvite decreases, sumption that the proportion of bromide in and rubidium in sylvite increases, in the upper Devonian sea water was the same as that of part of the section. In several cores this trend present-day sea water. This assumption is sup- begins at the base of zone 3. ported by the observation that bromide in (4) Carnallite contains more bromide than primary crystals of halite, from the base of the the halite and sylvite associated with it, and Prairie Evaporite, is approximately the same more rubidium than the sylvite. (from 0.003 to 0.007 weight percent) as that in (5) Major trends in profile for the increase primary halite from present-day sea water or decrease of bromide in halite are paralleled (Wardlaw and Schwerdtner, 1966). by similar trends for bromide in associated The assumption of similarity is applied also sylvite and carnallite. for the case of rubidium (observation 6, below), (6) There is greater variation of bromide in although in this case there is less substantiating sylvite than in associated halite or carnallite. evidence. Variation in the ratio of bromide in halite to (1) Carnallite consistently has greater than bromide in associated sylvite is about three the paragenetic proportion of bromide com- times as great as the variation in the cor- pared with associated halite. responding ratio for halite and associated (2) Red sylvite varies from having more carnallite. than, to having less than, the paragenetic pro- (7) Bromide is constant, or increases slightly portion of bromide compared with halite. upward, through massive carnallitite zones, but (3) Clear sylvite consistently has more there is a slight upward decrease of bromide in bromide than associated halite for paragenetic successive carnallitite zones. relationship. (8) The bromide and rubidium content of (4) Except for a few occurrences of clear minor traces of carnallite in halite units is sylvite, bromide in sylvite is consistently less similar to that of the massive carnallitite zones. than in carnallite. This is the reverse of the (9) Clear sylvite contains less than 0.003 paragenetic proportion. weight percent rubidium, whereas red sylvite (5) Bromide in halite, sylvite, and carnallite commonly contains more than this amount. of the potash zones of the Prairie Evaporite is below the range for primary salts fiom present- Generalizations from Trace-Element Profiles in day sea water (see Table 6). Relation to Experimental Data (6) Rubidium in carnallite is mainly within The paragenetic proportions of bromide in the primary range, in comparison with carnal-
A and B. Masses of sylvite elongate vertically and concentrated immediately above a layer of insolubles. From 6-29-30-21W2 at 3504 ft and 8-29-31-24W2 at 3494 ft, respectively/ C. Masses of carnallite elongate vertically and concentrated above a layer of insolubles. From 8-36-31- 25W2 at 3675 ft. D and E. Carnallite veins in masses of insolubles. The vein in E has core of carnallite surrounded by halite. From 5-15-30-23W2 at 3540 ft and 6-29-30-21W2 at 3601 ft. F. Mass of carnallite, elongate vertically, cutting through halite. From 1-27-31-16W2 at 3379 ft. G. Laminae of insolubles indicate inclination of bedding. Note irregular stringers of insolubles which are perpendicular to laminae and inclined to core axis. From 4-20-31-24W2 at 3732 ft. H. Vertically elongate carnallite selectively follows cleavage planes in large halite crystals. Irregular pockets are occupied by insolubles, sylvite, and carnallite in upward sequence.
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Br in halite Br in sylvite (red-rimmed variety) Br in sylvite (clear variety) Br in carnallite of cores Number Number Number Number from Watrous- Min. and of Min. and of Min. and of Min. and of Kandahar area Av. max. Range analyses Av. max. Range analyses Av. max. Range analyses Av. max. Range analyses 1-27-31-16W2 .012 .007-.013 .006 38 ,?nn .150-.303 .153 6 .142 .111-.200 .089 18 1-13-32-20W2 .011 .002-.020 .018 41 .110 .040-. 140 .100 9 .130 .120-.155 .035 6 .152 .125-.214 .089 7 6-29-30-2 1W2 .012 .004-.020 .016 52 .092 .022-.181 .159 11 .152 .100-.201 .101 5 .162 .120-.192 .072 25 16-10-30-22W2 .012 .002-.019 .017 59 .038 .018-.070 .052 7 .1-54 .060-. 183 .123 43 5-15-30-23W2 .010 .002-.019 .017 24 .081 .035-.130 .095 6 .132 .120-. 142 .022 4 5-14-31-24W2 .014 .003-.018 .015 28 .027 .019-.080 .061 8 .ISO .111-.163 .052 30 4-16-31-24W2 .010 .003-.015 .012 9 .150 .150 1 4-20-3 1-24W2 .011 .003-.030 .027 27 .075 .069-.090 .021 3 .103 .095-110 .015 2 8-29-3 1-24W2 .010 .004-.016 .012 24 .040 .018-.071 .053 4 .12 .100-.180 .080 4 15-33-3 1-24W2 .009 .002-.016 .014 34 .025 .011-.110 .099 14 4-10-32-24W2 .012 .003-.036 .033 33 .052 .016-.091 .075 11 1^0 .110-.183 .073 9 12-22-30-25W2 .010 .002-.020 .018 41 .100 .070-.132 .062 4 HS .130-. 140 .010 4 13-1 1-3 1-25W2 .011 .005-.015 .010 11 .052 .020-.172 .152 8 1 3-24-3 1-25W2 .011 .006-.018 .012 15 8-36-3 1-25W2 .011 .004-.030 .026 31 .110 .085-. 130 .045 5 ,116 .100-. 133 .033 3 Location of Cores outside Watrous- Kandahar area 4-22-21- 2W2 .009 .005-.030 .025 11 .120 .071-.170 .099 2 4-10-30- 8W2 .009 .005-.016 .011 73 .210 .160-.233 .073 9 1 3-22-28-1 1W2 .013' .005-.020 .015 21 .150 .080-.260 .180 7 IfiS .160-.172 .012 3 1-18-34-18W2 .006 .004-.010 .006 8 .076 .047-. 125 .078 fi 4-16-35-18W2 .009 .004-.015 .011 9 .073 .060-.091 .031 4 10] .042-.149 .107 19 9-27-16-20W2 .007 .001-.013 .012 109 .121 .065-. 150 .085 Ifi 1-26-17-24W2 .006 <.001-.016 .015 53 .073 .010-.156 .146 70 073 .072-.074 .002 3 6-25-37- 4W3 .011 .002-.017 .015 22 .044 .016-.122 .106 fi .140 .123-. 168 .045 8 3-28-39- 4W3 .012 .004-.020 .016 46 IDA .082-. 125 .043 17 —16-36- 3W3 .010 .006-.014 .008 32 .050 .016-.084 .068 28 Potash Company America Mine
* Note that averages are for the sections as a whole but that averages of ratios are for associated minerals.
WARDLAW, TABLE 4 Geological Society of America Bulletin, v. 79, no. 10
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TABLE 5. EXPERIMENTALLY DETERMINED BROMIDE RATIOS AND THOSE FOR PRAIRIE EVAPORITE
Halite Sylvite Carnallite Experimentally determined paragenetic proportions I 10 7 Proportions for Prairie Clear Red Evaporite Formation 1 13 to 20 5 to 22 8 to 22
lites from present-day sea water, but includes partition have not been investigated experi- higher values. mentally, but it is not expected that moderate (7) The amount of rubidium in red sylvite is pressures would cause appreciable effects in commonly several times greater than in the this system. Mclntire (1963) has reviewed the primary range, while the amount of rubidium thermodynamics of trace-element partition and in clear sylvite is mainly within, or less than, has discussed the effects of the various variables the primary range. on the numerical values of coefficients. The paragenetic proportions of bromide in Experimentally Determined Partition Coefficients halite, sylvite, and carnallite are given in Table for Bromide and Rubidium 5 (after Braitsch, 1962, p. 106-107). Braitsch The significance of the distribution of and Herrmann (1963) crystallized halite and bromide ions in solid phases of chlorides in carnallite separately, but Kiihn and Ritter (in relation to the solutions f om which they Kiihn, 1968) have subsequently investigated crystallize, has long been known, and it has the paragenetic ratios under conditions of been mentioned in several recent papers, paragenetic crystallization, at 30° C. Their Braitsch (1966, p. 293), Holser (1966, p. 248), results confirm the findings of Braitsch and Raup (1966, p. 236), Baar (1966, p. 276), and Herrmann. Wardlaw and Schwerdtner (1966, p. 332). Rubidium occurs in solid solution, substitut- The quantity of bromide in a chloride, or of ing for potassium in potassium minerals. rubidium in a potassium salt, bears a definite Partition coefficients for rubidium between relationship to the trace element content of the brines and carnallite have been experimentally parent brine. This relationship is expressed as a determined at 25° C and 83° C and show that partition coefficient which can be defined as: there is a large negative temperature coef- ficient for rubidium uptake by carnallite Weight percent trace element in (Braitsch, 1966, p. 298). At 25° C the partition the solid phase of a salt factor equals 22 ± 1 and at 83° C only 10 + 1. Weight percent trace element in the Kiihn (1963, p. Ill) reports a coefficient of ap- liquid phase from which the solid crystallized proximately 17 for rubidium in carnallite, at 30° C and with normal sea-water concentra- Interpretation of the genesis of salt rocks, tions of rubidium. The coefficient is said to from the occurrence of bromine and rubidium decrease with increasing concentration. Lainina in various phases in these rocks, is dependent on and Anoshin (1962) record a partition coef- the experimental determination of partition ficient of 66 for rubidium in carnallite at 16° C, coefficients for a variety of conditions. of 33 at 50° C, and of 16.5 at 75° C. Temperature, pressure, concentration of The partition coefficient for rubidium in trace element in solution, and presence of sylvite is about 2 and, according to Braitsch other ions in solution (particularly magnesium), (1966, p. 298), is not affected much by tem- affect the partition coefficients. The effects of perature. In contrast, Mclntire (1963, Table 5) these variables, with the exception of pressure, shows a distinct increase of rubidium uptake on the partition of bromide in chloride salts is by sylvite with rising temperature, from a documented by Braitsch (1962, p. 103-110) coefficient of 0.088 at 27° C to 0.146 at 100° C. and Braitsch and Herrmann (1963, p. 363- Kiihn (1963, p. 108) has indicated that sylvite 376). The effect of pressure on partition paragenetic with carnallite would have about coefficients depends on the difference between 1/11 of the rubidium content of carnallite. the partial molar volume of the trace element Although there are certain deficiencies and in the solid solution compared with the solu- inconsistencies in the partition data for tion. The effects of pressure on bromine rubidium in carnallite and sylvite, the available
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facts are of value in interpretation. The large b = partition coefficient for trace element in partition coefficient for rubidium in carnallite solid; means that, with progressive crystallization of _ weight of crystal precipitated carnallite from a brine, the brine will become weight of crystal precipitated impoverished in rubidium. Thus, in a normal + weight of water evaporated progressive evaporite sequence, rubidium in As Braitsch (1966, p. 298) has indicated, carnallite will decrease from oldest to youngest whether progressive crystallization will result beds. Solution and subsequent crystallization in enrichment or impoverishment of a trace of carnallite will cause enrichment of rubidium element in solution depends not only on the in carnallite. partition coefficient, but also on the fraction of As the partition coefficient for rubidium in crystals formed and of water evaporated. It sylvite is greater than unity (that is, approxi- depends on whether factor qb in the Boeke mately 2), it might be thought, from the defini- equation is less than, or greater than, 1. tion of the partition coefficient, that progres- Figure 7 illustrates the increase of rubidium, sive crystallization of sylvite from a brine from oldest to youngest sylvite, in a primary would lead to impoverishment of rubidium in sequence. Solution of sylvite and subsequent the brine, and therefore to subsequent crystal- crystallization, in contrast to the case for lization of sylvite. That this is not the case carnallite, would result in rubidium impoverish- becomes apparent from consideration of an ment in sylvite. equation which relates trace-element content in brine, and therefore in crystallizing solid, to System NaCl-KCl-MgClrH£> the stage of evaporation. An equation of this OA, in Figure 8, shows the ratio of magne- type is that of Boeke (1908), recorded in sium chloride to potassium chloride during the Braitsch and Herrman (1963, p. 294): stage of halite crystallization from magnesium- -Cl-cib) sulfate-deficient sea water. At 20° C, at point A, p = Pol JL\ sylvite crystallization begins and, with contin- ao / (1) ued evaporation, the composition of the brine where changes along line A-B as sylvite crystallizes. Point B lieson the boundary between the sylvite p = weight percent trace element in solution and carnallite fields. This is a reaction boundary, finally; and sylvite is unstable in the presence of brines po = weight percent trace element in solution in the carnallite and bischofite fields. Thus, with initially; further evaporation, unless the sylvite is re- ao = initial weight of solution; moved from contact with the brine, it will be a = final weight of solution; altered to carnallite. Carnallite crystallizes
TABLE 6. EXPERIMENTALLY DETERMINED BROMIDE AND RUBIDIUM IN PRIMARY HALITE, SYLVITE AND CARNALUTE, PROM MAGNESIUM SULFATE DEFICIENT SEA WATER, AND WEIGHT PERCENTAGES FROM PRAIRIE EVAPORITE SALTS * Range of Br in primary halite of potash zones 0.028 -0.053 Range of Br in halite of P. E. potash zones 0.001 -0.036 Range of Br in primary sylvite 0.289 -0.354 Range of Br in red sylvite of P. E. 0.010 -0.260 Range of Br in clear sylvite of P. E. 0.100 -0.303 Range of Br in primary carnallite 0.252 -0.382 Range of Br in carnallite of P. E. 0.042 -0.214 Range of Rb in primary sylvite 0.0017-0.002 Range of Rb in red sylvite of P.E. <0.001 -0.020 Range of Rb in clear sylvite of P.E. <0.003 Range of Rb in primary carnallite 0.0017-0.020 Range of Rb in carnallite of P.E. 0.004 -0.045
* Values expressed as weight percent. P.E. is abbreviation for Prairie Evaporite. Primary values from Braitsch (1962, p. 107, and 1966, p. 293).
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from the experimentally determined partition coefficients for bromide and rubidium in sylvite. The carnallite structure contains a significant amount of water, and, therefore, during the solution of carnallite, the volume of water in solution increases, thus promoting the further solution of carnallite. Carnallite will dissolve in fresh water, adding equal increments of magnesium and potassium chlorides, until the point of saturation with respect to potassium chloride, for a given temperature, is reached Figure 7. Trace-element distribution in salts of (point X, Fig. 8). Further solution of carnallite ideal profile. Mineral profile illustrates sequence of will result in precipitation of sylvite. salts crystallized during evaporation of 1000 cc Two different models can be visualized: one magnesium-sulfate-deficient sea water, at 25° C, in which a potassium-chloride-saturated solu- without subsequent reaction of salts and brines. tion is isothermally evaporated to precipitate Curves illustrate bromide and rubidium content sylvite, without further solution of carnallite; of the various salts crystallized during evaporation and another in which there is no evaporation (after Braitsch, 1962, p. 107; and 1966, p. 299). at saturation with potassium chloride, but Arrows indicate whether trace-element contents of particular salts would be increased or decreased by further leaching of magnesium chloride from solution in fresh water and subsequent crystalliza- tion. during evaporation to point D, where bischofite crystallization commences. Profiles 1 and 2 in Figure 8 show, respectively, the sequence of salts obtained from magnesium-sulfate-deficient sea water without and with reaction of sylvite at the reaction boundary. If carnallite is dissolved in water, magnesium chloride and potassium chloride enter the solution in equimolecular proportions, as il- lustrated by OX, Figure 8. At 20° C, X represents a saturation point for sylvite. If the solution is evaporated, sylvite will crystallize and the solution will change in composition along XB, to carnallite saturation at B. If solu- tion X is not evaporated, but exposed to more carnallite, magnesium chloride will continue to enter the solution, suppressing potassium chloride solubility and causing the precipitation of sylvite. With or without evaporation, then, carnallite will react with water to form sylvite. Thus, sylvite may alter to carnallite in the presence of magnesium chloride brines, or 0 10 20 30 40 carnallite alter to sylvite if treated with water MOL. K CI ond No Clj,/1000 MOL. H 0 » or a solution undersaturated with respect to 2 2 2 Z carnallite. Figure 8. The system Na2Cl2 — K2C12 — MgCl2 — H2O. Mineral profile 1 is for situation Bromide and Rubidium in Sylvite without reaction between sylvite and brine. Profile Derived from Carnallite 2 is for situation in which sylvite reacts with magnesium chloride brines to form carnallite. OA It is possible to determine the bromide and represents ratio of magnesium chloride to potassium rubidium content of sylvite, derived from chloride in present-day sea water (after Braitsch, carnallite with known bromide and rubidium, 1962, Fig. 9). Sylvite (solid line), carnallite (dashed by using the solubility data in Figure 8 and line), halite (dash-dot line).
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0 .01 .02 .03 .04 .05 0 .0! .02 .03 .04 .05 .06 .07 .08 .09 .10 .11 .12 .13 .14 .15 .16 .17 .18 .19 .20 WEIGHT % RUBIDIUM IN SYLVITE WEIGHT % BROMIDE IN SYUVITE Figure 9. Curves for bromide and rubidium in sylvite derived from carnallite by fresh-water leaching. The solid curves are for a model in which the volume of solution remains constant. The broken-line curves are for a decreasing-volume model in which no carnallite is dissolved after sylvite saturation is reached and the brine is evaporated to crystallize sylvite. Isothermal conditions of 25° C apply for both models.
carnallite, producing sylvite. Figure 9 il- crystallization (carnallite cannot be directly lustrates bromide and rubidium in sylvite, de- reworked in a similar way without first crystal- rived from carnallite with various initial lizing sylvite). bromide and rubidium contents, under the Alternative 1 is unlikely, in that sylvite and conditions of these two models. In either case, carnallite are far from being paragenetic with the sylvite deposited will have increasing respect to both bromine and rubidium (Tables amounts of trace elements as the process ad- 5 and 6). vances, as is illustrated by the curves presented. Alternative 4 is not considered likely, since At 20° C, sylvite deposition will cease when any solution of sylvite and subsequent crystal- magnesium chloride in the brine reaches a con- lization would diminish the rubidium content centration of 70 moles per 1000 moles water. below the primary range. Red sylvite has For example, carnallite with 0.2 weight per- anomalously high rubidium, commonly up to cent bromide dissolved in fresh water, will ten times greater than the maximum possible result in an initial sylvite with 0.047 weight per- for primary sylvite (Table 6). Similarly, alterna- cent bromide. Further leaching of carnallite, tive 2 provides no explanation of the anom- without any evaporation, will eventually re- alously high rubidium values for red sylvite. sult in sylvite with 0.1 weight percent bromide Carnallite, having a partition coefficient for at carnallite saturation (point B, Fig. 8). rubidium ten times that of sylvite, has, in the Figure 9 can be read in a similar way for initial stages of carnallite crystallization, ten rubidium and bromide in sylvite derived from times as much rubidium in solid solution as in carnallite, for the model in which evaporation preceding sylvite (Fig. 7). Were the sylvite to occurs. be derived from carnallite, by leaching of magnesium chloride, the sylvite could contain Relationship of Red Sylvite to Carnallite rubidium far in excess of the primary range of Four types of situations are considered: (1) values. Kiihn (1963, p. 107) has already Sylvite and carnallite are facies equivalents, postulated such a mechanism to account for having been deposited essentially contempora- high rubidium sylvites in certain German de- neously from brines of different salinity in posits. Alternative 3, then, provides the only different areas; (2) Sylvite reacted with satisfactory explanation of the anomalously magnesium chloride brines to form carnallite; high rubidium values in red sylvite. This al- (3) Magnesium chloride has been leached from ternative has been evaluated quantitatively. carnallite, to leave a residue of sylvite; (4) Figure 9 shows sets of curves which relate Sylvite, as presently found, is not directly re- the bromine and rubidium contents of carnal- lated to carnallite, but formed through solu- lite to those of sylvite derived by pure-water tion of pre-existing sylvite with subsequent leaching of magnesium chloride from carnallite.
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Table 7 presents the actual range of bromide ers (Valiashko, 1956, p. 182; Kiihn, 1955, p. 3; and rubidium in three cores for which detailed Borchert and Muir, 1964, p. 108) and has been analyses are available for associated red sylvite classed as a type of retrograde metamorphism. and carnallite. It also includes the range of bromide and rubidium in sylvite which would POTASSIUM-ARGON DATING result from leaching of carnallite to sylvite by pure water. Three samples of red carnallite and nineteen The theoretical values for bromide in derived of red sylvite were analysed by spectrometer sylvite tend to lie within the range of actual for their argon contents, in the Department of values for sylvite, or to be smaller than the Geology, University of Alberta. The three actual values. The altering solution probably carnallite samples gave dates of less than 7.5 was not pure water, but a brine with some m.y. It was apparent that during the outgassing bromide, which could account for the slightly operation preceding fusion, the crystal struc- higher range in the actual values. The range of ture was breaking down as water of hydration theoretical rubidium values corresponds closely came off the crystals, even at very low tempera- with the actual, suggesting that the rubidium tures. The carnallite dates are meaningless, content of the altering solution was small. since they merely indicate how much argon The actual situation is undoubtedly more happened to be retained in the carnallite complex than described here. It is possible, for sample during evacuation of the sample line example, that some of the high-rubidium prior to extraction. carnallite immediately underlying sylvite, as Results from the analysis of sylvite samples in 16-10-30-22W2, has been reworked and en- are given in Table 8. riched in rubidium, thus accounting for the The sylvite samples have an analytical error abrupt increase of rubidium in carnallite im- of + 10 m.y. The dates are minimum dates mediately underlying sylvite. with reference to stratigraphic location of the However, of the four types of relationship deposits. High argon pressures are needed to between sylvite and carnallite discussed, there force argon into the lattice of a crystallizing can be little doubt that alternative 3, the mineral, and it is unlikely that sylvite would derivation of sylvite from carnallite, accounts "build in" significant argon at crystallization most satisfactorily for the bromide and rubid- (A. Baadsgaard, 1966, oral commun.). The ium distribution between associated carnallite high proportion of radiogenic argon obtained and red sylvite. from the samples makes contamination of The derivation of sylvite by leaching of sylvite by argon improbable. carnallite is a process which has been recognized The oldest date, 339 m.y. (Mississippian), is in other deposits by Russian and German work- not far from the true age of the sample, which
TABLE 7. THEORETICAL BROMIDE AND RUBIDIUM WEIGHT PERCENTAGES IN SYLVITE DERIVED FROM CARNALLITE COMPARED WITH ACTUAL VALUES FOR PRAIRIE EVAPORITE *
5-14-31-24W2 6-29-30-2 1W2 16-10-30-22W2 Actual Br in carnallite from Prairie Evaporite 0.11-0.15 0.147-0.166 0.074-0.086 Theoretical range of Br in sylvite derived from carnallite with above Br content (leaching by pure water) 0.026-0.075 0.035-0.083 0.017-0.044 Actual range of Br in red sylvite associated with carnallite 0.019-0.08 0.105-0.160 0.018-0.070 Actual Rb in carnallite from Prairie Evaporite 0.024-0.029 0.013-0.014 0.014-0.021-(.036) Theoretical range of Rb in sylvite derived from carnallite with above Rb content (leaching by pure water) 0.002-0.014 0.003-0.017 0.004-0.017-(.044) Actual range of Rb in red sylvite associated with carnallite 0.0034-0.012 0.004-0.008 0.005-0.015
* Bracketed figures for rubidium in carnallite from 16-10-30-22W2 represent two values anomalously higher than other values from associated carnallite in the same core (see Pi. 1).
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TABLE 8. POTASSIUM-ARGON AGE DATES FROM SAMPLES OF SYLVITE*
Depth Zone and Type Date Location Subsurface of Sylvite (millions of years) Period International Minerals Mine Zone 1 ? Esterhazy— 19-33W1 3132 Red 207 Triassic Zone 2 1-27-3 1-1 6W2 3356 Clear 325 Mississippian Zone 1 1-27-31-16W2 3451 Clear 56 Tertiary Zone 1 1-27-31-16W2 3454 Clear 333 Mississippian Zone 1? 9-27-16-20W2 5477 Red 222 Permian Zone 3A 1-13-32-20W2 3158 Red 297 Permian Zone 1 1-13-32-20W2 3326 Clear 248 Permian Zone 3A 6-29-30-2 1W2 3485 Red 295 Permian Zone 1 6-29-30-21W2 3655 Clear 262 Permian Zone 3B 16-10-30-22W2 3462 Red 256 Permian Zone 3B 16-10-30-22W2 3470 Red 339 Mississippian Zone 3B 16-10-30-22W2 3471 Red 272 Permian Zone 2 16-10-30-22W2 3614 Clear 318 Pennsylvanian Zone 3B 5-14-3 1-24W2 3380 Red 289 Pennsylvanian Zone 2 5-14-31-24W2 3523 Clear 318 Pennsylvanian Zone 3B 8-29-3 1-24 W2 3491 Red 344 Mississippian Zone 3B 15-33-31-24W2 3378 Red 334 Mississippian Zone 3B 13-1 1-3 1-25 W2 3644 Red 315 Mississippian Zone 2 8-36-3 1-25 W2 3632 Red 128 Cretaceous * Analytical error of ± 10 m.y.
is about 370 m.y. (Middle Devonian, from leaching of carnallite to sylvite was not as- fossil evidence). sociated with the extensive Cretaceous, and Of the nineteen age determinations, seven- possibly post-Cretaceous, episodes of salt teen range from Mississippian to Triassic and solution in the area. two are younger, one Cretaceous and one Tertiary. No explanation can be offered for CONCLUSIONS these two anomalous ages. There is no significant Potash zone 1 consists of clear sylvinite. The difference between the ages of the clear and red clear, anhedral sylvite grains commonly are varieties of sylvite, although petrographic rimmed by carnallite, extensions of which occur evidence indicates that the clear variety is preferentially along halite and sylvite cleavages older. There is no apparent correlation between and halite-sylvite grain boundaries. These re- depth, or stratigraphic position of sample, and lationships suggest that carnallite is replacing age based on potassium-argon analysis. sylvite and halite and that the clear sylvite It may be concluded that the red sylvite, grains are resorption shapes. Presumably, and therefore the alteration of red carnallite sylvite reacted with brines enriched in magne- to red sylvite, occurred in pre-Triassic time. sium chloride, the carnallite rims which formed This substantiates the conclusion that the having inhibited further reaction of sylvite
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with the brine. It is not known whether or not the total Prairie Evaporite is thicker in local the magnesium chloride brines are genetically regions of carnallitite than in adjacent regions related to those from which the clear sylvite of sylvinite. The total thickness of Prairie originally crystallized. Evaporite salts can be determined by seismic The replacement of halite by carnallite is techniques, and this provides a valuable pros- less simple to explain, since it is not possible to pecting guide to the presence of local areas of dissolve halite and precipitate carnallite from a carnallitite. single solution. Alteration of red carnallitite to red sylvinite Clear sylvite, in contrast to the more abun- presumably occurred from the top down, since dant red sylvite in zones 2 and 3, consistently sylvinite overlies carnallitite. The downward has less than 0.003 weight percent rubidium, movement of magnesium- and potassium-bear- and in several samples there is less than 0.001 ing brines is suggested by the elongate, ver- weight percent rubidium. tically-oriented stringers of carnallite and Red sylvinite and massive red carnallitite sylvite and by the presence of local pockets of occur in zones 2 and 3, but not in zone 1. these minerals overlying, but not underlying, Abrupt vertical and lateral changes from red laminae of insolubles. carnallitite to red sylvinite are common. Red Seventeen potassium-argon dates on the sylvinite overlies red carnallitite, both in the sylvite range from Mississippian to Triassic; section as a whole, and within individual zones two samples gave younger ages. These are where both types occur. This is the reverse of a minimum ages and indicate that all but two of normal depositional sequence. the sylvite grains are Permian or older. It may Red sylvite rims red carnallite, and ex- be concluded that the red sylvinite, and there- tensions of sylvite lie along preferred crystal- fore the alteration of red carnallite to red lographic planes in carnallite. Iron oxide in- sylvite, occurred in pre-Triassic time. This clusions are evenly distributed throughout supports the conclusion that the leaching of carnallite grains, and have a preferred orienta- carnallite to sylvite was not associated with the tion in relation to the crystallographic axes of extensive Cretaceous, and possibly post- carnallite. Similar inclusions occur in sylvite, Cretaceous, episodes of salt solution in the area. but generally are restricted to the margins of The alteration of carnallite to sylvite may have sylvite grains, where they are oriented ran- been essentially contemporaneous with the domly. It appears that red sylvite has replaced deposition of the potash zones, because in one carnallite and inherited iron oxide inclusions core (4-29-32-22W2, Fig. 3) the upper por- from carnallite. tions of zones 2 and 3A are sylvinite and the The large amount of rubidium in red sylvite, lower portions are carnallitite. Had the altera- as much as ten times the maximum for primary tion occurred from the top down after the sylvite, can be accounted for if the sylvite was deposition of all potash zones, one contact derived from red carnallite. It cannot be ac- between red sylvinite and red carnallitite, counted for if sylvite and carnallite are facies rather than two, might have been expected. equivalents, crystallized from related brines, or The potash zones are succeeded by halite if sylvite formed by solution and subsequent zones which were deposited from brines under- crystallization of sylvinites. Bromide in red saturated with respect to potassium and magne- sylvite is consistent with the interpretation that sium chloride. In contact with carnallite, these it was derived from red carnallite. Petrological brines would leach magnesium chloride and and geochemical data both indicate that red leave a residue of sylvite. Alternatively, it is sylvinite was formed by the leaching of possible that carnallite was leached by direct magnesium chloride from red carnallitite. rainfall, or by runoff from adjacent exposed A comparison of the proportions of carnallite land areas. and sylvite, in a given potash zone, from a re- Bromide in halite, sylvite, and carnallite, in gion of carnallitite to an adjacent region of the potash zones, is consistently less than the sylvinite, reveals that the amount of sylvite primary range of values for salts from present- present corresponds to the amount which could day sea water, a fact previously recorded by be derived from carnallite by leaching of Schwerdtner (1964, p. 1108). Either the magnesium chloride. Potash zones 2 and 3 are bromide to chloride ratio, in the brines from cumulatively about 50 ft thicker where they which they formed, was lowered by addition of are massive red carnallitite than where they solutions from previously deposited salts, or are sylvinite. In the Watrous-Kandahar area these minerals were equilibrated with meta-
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morphosed brines. Ktihn (1968) has demon- content below primary levels, but such a proc- strated that halite and sylvite will equilibrate ess would also greatly enrich rubidium in the with a saturated brine which is other than carnallite. One explanation is that the carnal- paragenetic with respect to bromide. In this lite has equilibrated with a brine having less way, the trace-element content of a grain can than the primary range of bromide. It is be changed without solution of the grain. necessary to assume either that such a process Extensive equilibration could not have oc- of equilibration did not affect rubidium in curred during the final formation of these carnallite, or that the altering solution had rocks, since halite, sylvite, and carnallite are much the same rubidium content as the parent nonparagenetic with respect to bromide and brine from which carnallite formed, rubidium. Traces of carnallite in halite underlying red Rubidium in red carnallite is mainly in the carnallitite zones con tain bromide and rubidium primary range, but bromide is less than the in the same range as in the overlying carnallite. primary range. This situation has not been These traces of carnallite probably crystallized accounted for satisfactorily. Solution of carnal- from genetically related brines which descended lite and redeposition would reduce the bromide the section.
REFERENCES CITED American Society for Testing and Materials, 1963, Powder diffraction file, Thirteenth set: Special Tech- nical Publication no. 48-M. Baar, C. A., 1966, Bromine investigations on eastern Canada salt deposits, p. 276-292 in Symposium on Salt: Cleveland, Ohio, Northern Ohio Geol. Soc. Inc., 443 p. Bishop, R. A., 1954, Saskatchewan exploratory progress and problems, in Western Canada Sedimentary Basin: Am. Assoc. Petroleum Geologists, Rutherford Memorial Volume, p. 474-485. Boeke, H. D., 1908, Uber das Kristallisationsschema der Chloride, Bromide, Jodide von Natrium, Kalium und Magnesium: Zeitschr. Kristallographie, v. 45, p. 346-391. Borchert, H., and Muir, R. O., 1964, Salt Deposits: London, Van Nostrand, 338 p. Braitsch, O., 1962, Entstehung und Stoffbestand der Salzlagerstatten, Mineralogie und Petrographie in Einzeldarstellungen, Springer-Verlag, Berlin, 232 p. 1966, Bromine and Rubidium as indicators of environment during sylvite and carnallite deposition of the upper Rhine Valley evaporites, p. 293-301 in Symposium on Salt: Cleveland, Ohio, Northern Ohio Geol. Soc. Inc., 443 p. Braitsch, O., and Herrmann, A. G., 1963, Zur Geochemie des Broms in salinaren Sedimenten. Teil 1: Experimentelle Bestimmung der Br-Verteilung in verschiedenen natiirhchen Salzsystemen: Geochim. et Cosmochim. Acta, v. 27, p. 361-391. D'Ans, J., and Hbfer, P., 1934, Untersuchungen an Brom: Angew. Chemie, Jahrg., v. 47, no. 5, p. 71-74- Dreimanis, A., 1962, Quantitative gasometric determination of calcite and dolomite by using Chittick apparatus: Jour. Sed. Petrology, v. 32, no. 3, p. 520-529. Fischer, W., 1959, Strukturuntersuchung an synthetischem carnallit: Ph.D. thesis, University of Kiel, Germany. Goudie, M. A., 1957, Middle Devonian potash beds of central Saskatchewan: Saskatchewan Department of Mineral Resources, Unpub. Rept., 81 p. Holser, W. T., 1966, Bromide geochemistry of salt rocks, p. 248-275 in Symposium on Salt: Cleveland, Ohio, Northern Ohio Geol. Soc. Inc., 443 p. Kurd, D., and Shaw, 1966, The carnallite problem in the Saskatchewan potash field—some empirical re- lations as determined by seismic isopachs: Mining Eng., v. 18, no. 8, p. 44 (abs. only). Johnsen, A., 1909, Beitrage zur Kenntnis der Salzlager I. Regelmassige Verwachsung von Carnallit und Eisenglanz: Cbl. Mm., p. 168-173. Kiihn, R., 1955, Uber den Bromgehalt von Salzgesteinen, insbesondere die quantitative Ableitung des Bromgehaltes nichtprimarer Hartsalze oder Sylvinite aus Carnallit: Kali u. Steinsalz, v. 1, h. 9, p. 3. 1963, Rubidium als geochemisches Leitelement bei der lagerstattenkundlichen Charakterisierung von Carnalliten und natvirlichen Salzlosungen: Neues Jahrb. Mineralogie Monatsh., no. 5, p. 107-115. 1968, Geochemistry of the German potash deposits: Internal. Conf. on Saline Deposits, Houston, Tex: Geol. Soc. America Spec. Paper 88.
Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/79/10/1273/3427908/i0016-7606-79-10-1273.pdf by guest on 03 October 2021 1294 N. C. WARDLAW—CARNALLITE-SYLVITE, SASKATCHEWAN
Lainina, I. N., and Anoshin, G. N., 1962, Some regularities of distribution of rubidium, thallium and bromine in the process of formation of potassium salt deposits: Akad. Nauk, S.S.S.R., Sibir. Sekt., Geol. and Geophys., no. 3, p. 64-74 (in Russian). Mclntire, W. L., 1963, Trace element partition coefficients—a review of theory and applications to geology: Geochim. et Cosmochim. Acta, v. 27, p. 1209-1264. O'Donnell, R. W., 1966, Separation and extraction of the alkali metal halides from Saskatchewan potash: M.Sc. thesis, Dept, of Chemistry and Chemical Engineering, University of Saskatchewan, Saskatoon, 132 p. Raup, O. B., 1966, Bromine distribution in some halite rocks of the Paradox Member, Hermosa Formation, in Utah, p. 236-247 in Symposium on Salt: Cleveland, Ohio, Northern Ohio Geol. Soc. Inc., 443 p. Schaller, W. T., and Henderson, E. P., 1932, Mineralogy of drill cores from the potash field of New Mexico and Texas: U.S. Geol. Surv. Bull. 833, 124 p. Schwerdtner, W. M., 1963, Analysis of small amounts of bromides in the presence of large amounts of chlorides, p. 247-248 in Symposium on Salt: Cleveland, Ohio, Northern Ohio Geol. Soc., Inc., 661 p. 1964, Genesis of potash rocks in Middle Devonian Prairie Evaporite Formation of Saskatchewan: Am. Assoc. Petroleum Geologists Bull., v. 48, no. 7, p. 1108-1115. Seifert, H., 1937, Die anomalen Mischkristalle: Fortschr. Min., v. 22, p. 185-488. Spangenberg, K., and Neuhaus, A., 1930, Kiinstlich gefarbte Kristalle als Beispiele sogenannter anomaler Mischkristalle und ihr mineral-chemische Bedeutung: Chemie D. Erde no. 5, p. 437-528. Valiashko, M. G., 1956, Geochemistry of potash deposits: Doklady Akad. Nauk, SSSR, p. 182. Wardlaw, N. C., and Schwerdtner, W. M., 1963, Koenenite from Saskatchewan, Canada: Neues Jahrb. Geologic u. Pala'ontologie Monatsh., v. 2, p. 76. 1966, Halite-anhydrite seasonal layers in the Middle Devonian Prairie Evaporite Formation, Sas- katchewan, Canada: Geol. Soc. America Bull., v. 77, p. 331-342.
MANUSCRIPT RECEIVED BY THE SOCIETY MAY 25, 1967 REVISED MANUSCRIPT RECEIVED NOVEMBER 17, 1967
Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/79/10/1273/3427908/i0016-7606-79-10-1273.pdf by guest on 03 October 2021 PHOTOMICROGRAPHS OF SYLVITE AND CARNALLITE Figure 1. Goethite fibers, with preferred alignment, and hematite plates in carnallite. Plane-polarized. Location 12-22-30-25W2 at 3856 ft. Figure 2. Goethite fibers, randomly arranged, near margin of sylvite grain. Plane-polarized. Location 12-22-30-25W2 at 3856 ft. Figure 3. Contact between sylvite (S) and carnallite (C) with trains of hematite and goethite inclusions crossing grain boundary. Plane-polarized. Location 16-10-30-22W2 at 3469 ft. Figure 4. Same as Figure 3, but with nicols crossed. Black area is sylvite. Figure 5. Hematite and goethite inclusions concentrated along contact between sylvite (S) and carnal- lite (C). Similar inclusions occur randomly near margin of sylvite grain (arrows). Plane-polarized. Location 12-22-30-25W2 at 3856 ft. Figure 6. Carnallite (C) margined by red-rimmed sylvite (S). Processes of sylvite tend to follow in- clusion planes in carnallite. Halite (H) is euhedral to insolubles (I). Plane-polarized. Location 12-22-30- 25W2 at 3856 ft.
WARDLAW, PLATE 2 Geological Society of America Bulletin, vol. 79, no. 10
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WARDLAW, PLATE 2 Geological Society of America Bulletin, v. 79, no. 10
Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/79/10/1273/3427908/i0016-7606-79-10-1273.pdf by guest on 03 October 2021 PHOTOMICROGRAPHS OF HALITE, SYLVITE, AND CARNALLITE Figure 1. Gradation from dark hematite inclusions in parallel planes through sylvite (at right) to hematite inclusions concentrated near sylvite grain boundaries (at left). Plane-polarized. Location 16-10- 30-22W2 at 3469 ft. Figure 2. Wisps of hematite in sylvite (S) radiate from inclusions (I) of insolubles. Plane-polarized. Location 12-22-30-25W2 at 3894 ft. Figure 3. Portions of carnallite (C), with common orientation, isolated in halite (H). Processes of halite penetrate along fractures and inclusion planes in carnallite. Plane-polarized. Location 16-10-30- 22W2 at 3579 ft. Figure 4. Halite (H) penetrating selectively along inclusion planes in carnallite (C). Plane-polarized. Location 16-10-30-22W2 at 3643 ft. Figure 5. Sylvite grains (S) with dark hematite and goethite rich margins. Large halite gram (H) with three patches of sylvite having common orientation, and with hematite-goethite rims (arrows) on one side only. Plane-polarized. Location 12-22-30-25W2 at 3894 ft. Figure 6. Rounded halite grains in a matrix of fine carnallite grains, which appear to "wrap around" halite. Plane-polarized. Location 4-20-31-24W2 at 3635 ft.
WARDLAW, PLATE 3 Geological Society of America Bulletin, v. 79, no. 10
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WARDLAW, PLATE 3 Geological Society of America Bulletin, v. 79, no. 10
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