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John Warren - Wednesday, October 31, 2018 BrineSalty evolution Matters & origins of pot- ash ore : Primary or second- ary? Part 1 of 3 Introduction as in the Permian, when MgSO4 bittern salts are typical There is a dichotomy in mineralogical associations and co-precipitates with sylvite/ (Figure 1b). precipitation series in both modern and ancient ore The validity of the ocean argument is primar- deposits. Interpretations of ancient potash ore mineralo- ily based on determinations of inclusion chemistries as gies across time are generally tied to the evolution of the measured in chevron (Figure 1a; Lowenstein et al., hydrochemical proportions in modern and ancient oceans. 2014). Inclusions in growth-aligned primary chev- We have already discussed this in previous Salty Matters rons are assumed to preserve the chemical proportions of articles and will not reperat the detail here (see August 10, the ambient oceanic precipitating the halite. That 2015; July 31, 2018). is, the working assumption is that pristine aligned-halite At times in the past, such as in the Devonian and the Cre- chevrons have not been subject to significant diagenetic tacous, the world ocean was depleted in the Mg and SO4 alteration once the was deposited and permeability was relative to the present-day ocean (Figure 1a). In the rele- lost due to ongoing halite cementation in the shallow (eo- vant literature this has led to the application of the term genetic) subsurface realm. MgSO4-depleted versus the MgSO4-enriched oceans. In The same assumption as to the pristine nature of chev- terms of brine evolution, this is related to the gypsum di- ron halite is applied to outcomes of biological experiments vide, with the term MgSO4-enriched used to describe the where Permian archaeal/halobacterial life has been re-an- ocean chemistry of today and other times in the past, such imated using ancient salt samples (Vreeland et al., 2000).

A. MgSO4 MgSO4-free MgSO4 MgSO4-free MgSO4 B. Ar. ? Calcite Aragonite ? Calcite ? Ar. CaCl ocean CaCl ocean 5 2 2 Evaporative concentration Modern Mg/Ca 40 of a marine brine

O) Modern SO 2 Ca 4 4 Precipitation The of CaCO CaCO

oceans 3 3 30 2 divide HCO ->Ca2+ Ca2+>HCO - 3 CaCl 3 3

mmol/(kg H Alkaline brine Precipitation 4 of gypsum 20 Na-K-Mg The 2 Cl-SO -CO CaSO .2H O No 4 3 4 2 gypsum gypsum Archean Phanerozoic seawater

4 divide Mg/Ca

Carb. Mg/Ca (molar) Mg/Ca Carb. 2- 2+ 2+ 2- Ca and SO SO >Ca Ca >SO 10 1 4 4 MgSO oceans MgSO bittern 4 CaCl2 bittern SO4 Modern Ca Na-K-Mg Na-K-Mg-Ca MgSO4ocean Cl-SO4 Cl Pre-C C Ord S D M P Pm Tr J K Pg Ng 0 MgSO4-enriched seawater MgSO4-depleted seawater 600 500 400 300 200 100 0 Age (Ma)

Figure 1. Evolution of Phanerozoic seawater. A) Secular variation in the amounts of Ca and SO4 in seawater for the last 600 my estimated from fluid inclusions in marine halites (vertical bars), compared to predicted seawater secular variations. The horizontal line around 20 mml/kg H2O is the approximate divide between MgSO4-enriched and MgSO4-depleted seas. Also plotted are the temporal distributions in the primary miner- alogies of Phanerozoic nonskeletal carbonates (calcite and aragonite) and periods of MgSO4-free versus MgSO4 bitterns. For Mg/Ca, the grey vertical plot bars are from halite inclusions measurements but the grey Mg/Ca curve is from marine carbonate data (after Lowenstein et al., 2001,

2003; with Paleozoic MgSO4 boundary change after Holt et al., 2014). B) Chemical divides and the evolution of three major brine types in the framework of evolving oceanic chemistry (in part after Hardie, 1984).

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Primary potash ore? gurian diapirs of the Cis-Urals of Russia and the Devonian But does the same assumption of pristine texturing across diapirs of the Pripyat basin . time also apply to the halite layers associated with the And so, herein lies the main point of discussion for this world’s potash ores? In my experience of subsurface potash and the next two Salty Matters articles, namely, what, ores and their textures, I have rarely seen primary-chev- where and when is(are) the mechanism(s) or association(s) ron halite interlayered with potash ore layers of either of hydrochemical mechanisms that sufficiently concentrate sylvite or carnallite. An obvious exception is the pristine or alter a brine’s chemistry to where it precipitates eco- interlayering of chevron halite and sylvite in the now-de- nomic levels of a variety of potash salts, as either muriate of pleted Eocene potash ores of the Mulhouse Basin, France potash or sulphate of potash. Notably, there are no Quater- (Lowenstein and Spencer, 1990). There, the sylvite layers nary-age solid state ore systems that are mined for potash. intercalate at the cm-scale with chevron halite, and the al- In this article, we look at the main modern brine systems ternating layering is thought to be related to precipitation where muriate of potash (MOP) is produced economical- driven by temperature fluctuations in a series of shallow ly by solar evaporation (Salar de Atacama, Chile; Qarhan density-stratified meromictic brine (documented in sump, ; and the southern Basin of the Dead Sea). next Salty Matters article). In the second article we will focus on sulphate of potash More typically, ancient potash ore textures are diagenetic (SOP) production in Quaternary saline sumps (Great Salt and indicate responses to varying degrees of dissolution, , USA and Lop Nur, China). In the third article we brine infiltration and alteration. The simpler styles of brine shall discuss depositional and diagenetic characteristics of infiltration consist of a background matrix dominated by solid-state potash ores some of the world’s larger deposits cm-dm scale chevron halite layers that has been subject (e.g. Devonian of western Canada) and relate the observa- to dissolution and karstification during shallow burial.Re- tions of ancient potash textures to time-based evolution of sultant cm-dm scale voids typically retain a mm-thick sel- potash precipitating , and subsequent alteration or vedge of CaSO4 lathes and needles, followed by fill of the the ore textures, which are typically driven by later cross- remaining void by varying amounts of sparry halite, carnal- flushing by one or more pulses of diagenetically-evolved lite and sylvite. This type of texture dominates in Quater- brines. nary stratoid potash layers in the southern in China and the Cretaceous carnallite-rich layers of the Potash from brine in Salar de Atacama Maha Sarakham Fm in NE Thailand and southern China (MOP in a simple near-uniserial set of (Warren, 2016). Then there are the even more altered and recrystallised, but still bedded, textures in the potash ore brine concentration pans) zones of Devonian Prairie Evaporite of western Canada Potash production in Salar de Atacama is a byproduct of (Wardlaw, 1968) and potash layers in the Permian Basin in the production of carbonate from shallow lake west Texas and New Mexico (Lowenstein, 1988; Hot and brines pumped into a series of solar concentration pans Powers, 2011). Beyond this level of diagenetic texturing (Figure 2). The inflow feed to the concentrator pans comes are the flow-orientated and foliated structural textures of from fields of brine wells extracting pore waters from the the Permian potash ores in potash mines in the diapiric salt nucleus facies in the central and southern part of the Zechstein evaporites of Germany and Poland, the Kun- Atacama saltflats (Figure 3a,b). However, Atacama pore

A. B.

Figure 2. Bine production well networks and saltfields in Salar de Atacama, Chile. A) View of the SQM brine field where saline brine is pumped to the surface and into nearby solar evaporation pans. B) Solar evaporation pans at the Rockwood Lithium saltworks , pans showing yellow-green coloration where liquours are approaching lithium carbonate saturation (≈6000ppm) and are ready to be pumped to the brine processing plant. Page 2 www.saltworkconsultants.com

68° 30’ 68° 15’

Vilama 23° 2 A. River B. C. San Pedro River 0 Sulphate Zone Llano de la 23°

15’ Domeyko Range Paciencia salar log Li (mmol/L ) -2 Tatio

geyser Silty salar crust Cordillera de la Sal -4 0 1 2 3 4 Solar 23° Halite Zone log Na (mmol/L) pans 30’ San Pedro River and tributaries Vilama River and tributaries 0 20 Tatio geyser km Northeastern in ows Southeastern in ows Península Atacama and marsh de Chépica 23° 45’ Artesian wells 10 km ANDEAN ALTIPLANO Llano de la Paciencia salar

Figure 3. Saline brines in Salar de Atacama, Chile. A) General overview of Salar de Atacama, Chile, showing centripetal endorheic drainage (Bing® image scaled and mounted in MapInfo). B) Surface geology showing nearby Neogene evaporite outcrops in the Cordillera de la Sal. C) Lithium content of wells in the halite nucleus and other nearby brine sources (after Carmona et al., 2000). brines are not chemically homogeneous across the salar sium, then then sulphate in the more saline (Alonso and Risacher, 1996; Carmona, 2002; Carmona et regions of the salar sump (Figure 4; Lowenstein and Ri- al., 2000; Pueyo et al. 2017). The most common prima- sacher, 2009). In addition, owing to the progressive reduc- ry inflow brines to the Atacama sump are sulphate-rich tion of porosity in depth driven mainly by diagenetic halite

(SO4/Ca > 1), but there are areas in the salt flat at the cementation, the pore brine in the upper 40 meters of the southern end of the playa, such as those near the Península salar sediment column accumulates by advection in the de Chépica, where pore brines are richer in (SO4/ area of greatest porosity, i.e., in this top 40 m of sediments Ca < 1; Figure 4). These brines also contain elevated levels of the salt flat at the southern end of Atacama (Pueyo et of lithium (Figure 3c; Risacher et al., 2003). al., 2017). When pumped from the hosting salar sediments into the concentrator pans the final brines contain elevated Ion proportions in the natural salar inflow and pore waters levels of lithium (≈ 6000 ppm). These lithium-en- are dominated by sodium and chloride, followed by potas-

104 Salar de Atacama Na 3 Mg 10 K Ca 102

101 SO4 HCO3

Ions (mMol/L) 1

10 1 Salt Nucleus

10 2 Margin and springs 0 1000 2000 3000 4000 5000 6000 Cl (mMol/L) Figure 4. Hydrogeochemistry of various inflow and saltflat porewaters in Salar de Atacama, Chile (replotted from Table 4 in Lowenstein and Risacher, 2009) Page 3 www.saltworkconsultants.com

Inflows Concentrators

Halite Carnallite Sylvite Bischofite 90,000 Na

80,000 Mg 1 Well Pond 9 Pond K 17 Pond

70,000 Ca 8 Pond Pond 15 Pond SO4 Ditch 4 Ditch

60,000 Li 13 Pond Pond 13/14 Pond B 11 Pond

50,000 20 Well

40,000 6 Pond

30,000 Concentration (mg/L)

20,000

10,000

0 1.5 105 2.0 105 2.5 105 3.0 105 3.5 105 4.0 105 A. Cl (mg/L) Concentrators 8

6 pH

4 Halite

2 Sylvite 0.6 Carnallite Bischofite Pond 17 Pond

0.4 15 Pond Pond 13 Pond Pond 9 Pond Pond 13/14 Pond ater activity Pond 11 Pond

W 0.2 Pond 8 Pond Pond 6 Pond 0 2.0 105 2.5 105 3.0 105 3.5 105 4.0 105 B. Cl (mg/L) Figure 5. Brine evolution in the Atacama pans (replotted from data in tables in Pueyo et al., 2017). A) Mineral precipitation suites tied to ionic proportions in the evolving pan brines. B) Mineral precipitates tied to evolving pH and decreasing water activity. Note the high acidities obtained in the bischofite precipitating ponds. riched acidic waters are then pumped to a nearby industri- bittern paragenesis of salts precipitate that is mostly de- al plant and processed to obtain lithium carbonate as the void of magnesium sulphate salt due to the low levels of main commercial product. sulphate attained in the various concentator pans via wide- spread precipitation of gypsum in the early concentrator In a benchmark paper, Pueyo et al. (2017) document the pans (Figures 4, 5). brine evolution and products recovered in the solar pans of Rockwood Lithium GmbH (Figure 2b; formerly Sociedad The depletion of sulphate levels in the early concentrators Chilena del Litio) in the Península de Chépica. There, a is done via artifical manipulation of ionic proportions in Page 4 www.saltworkconsultants.com

the feeders. Without alteration evaporation of the main the last ponds (R-1 to R-3), whose volumes undergo a re- natural salt flat brine feeds, which are rich in sulfate, would duction to 1/50th of the starting volume, are treated at the result in assemblages that, in addition to , would factory to obtain lithium carbonate as the main commer- contain contain problematic magnesium sulfates (such as cial product. schoenite, kainite, glaserite as in Great ). The As documented in Pueyo et al. (2017), the average daily presence of such sulphate salts and ions in the liquor feed temperature in the Salar de Atacama ranges between 22 °C to the lithium carbonate plant would complicate the lith- in February and 8 °C in July, with a maximum oscillation ium carbonate extraction process. So the aim is to remove of approximately 14 °C. Wind speed ranges daily from< 2 most tof the sulphate via constructing a suitably balanced −1 −1 ms in the morning to 15 ms in the afternoon. Rainfall chemistry in the early concentrator brine stage (aompare in the area of the salt flat corresponds to that of a hyper- ionic proportions in sulphate between Figure 4 and Figure arid desert climate with an annual average, for the period 5). 1988–2011, of 28 mm at San Pedro de Atacama, 15.1 mm Such a sylvite/carnallite brine paragenesis, sans sulphate at Peine and 11.6 mm at the lithium saltworks, in the last (as seen in Figure 5), is similar to that described in an- case ranging between 0 and 86 mm for individual years. cient Mg-sulphate-free marine potash deposits (Braitsch, The adjoining Altiplano to the east has an arid climate with 1971). That is, as the brines pass through the concentra- an average annual rainfall of approximately 100 mm. The tors with successive pans transitioning to higher , average relative humidity in the saltpan area, for the period the potash salts carnallite and sylvite precipitate, without 2006–2011, is 19.8% with a maximum around February the complication of the wide- spread magnesium sulphate salts that complicate the processing of A. marine-derived bitterns and typ- 16 ify SOP production in the Og- den Salt flats, with their feed of Pore brines pumped from brine eld wells Great Salt Lake brines. Relative that penetrate the H = Halite porous upper 40m proportions of sulphate are much Gy = Gypsum H of salar sediment higher in the Great Salt Lake Sy = Sylvite Cn = Carnallite brine feed (see later section). 14 Bi =Bischo te H Cn = Lithium carnallite The balance is accomplished by Li 17 mixing a Ca-rich brine with the H+Gy natural SO4-brine in an appro- Li Li Li priate ratio. These modified pore R-3 Bi Bi Bi Sy Sy Sy Cn

brines are then pumped and H+Sy R-2 Cn+Bi Sy+Cn Bi+Cn Bi+Cn Bi+Cn discharged into the early ponds 13 12 11 10 9 8 7 6 5 4 3 2 1 Pore brine from R-1 100 m of the saltwork circuit (ponds nearby ditch N number 17 and 16, as seen in Figures 5 and 6). In these ponds, B. halite precipitates from the very Pond No. beginning with small amounts 14 14-13 of accessory gypsum as brines 222,400 gypsum are saturated with both miner- halite 13 anhy. als. Subsequently, the brines are 224,700 transferred to increasingly small- sylvite er ponds where halite (ponds 15 10 and 14), halite and sylvite (pond 13), sylvite (ponds 12, 11 and 10), 9

Increasing 295,150 sylvite and carnallite (pond 9), 8 carnallite (pond 8), carnallite and 332,500 carnallite 7 bischofite bischofite (pond 7), bischofite 6 (ponds 6, 5 and 4), bischofite 381,150 0 10 20 30 40 50 60 70 80 90 100 with some lithium-carnallite Mineral percentage

[LiCl·MgCl2·6H2O] (pond 3), Figure 6. Mineral precipitation series in Rockwood pans, Salar de Atacama (replotted from tables Pueyo et al., 2017). A) Plan view of mineral pans showing dominant mineral precipitates in pans 17 to 1. B) and lithium-carnallite (ponds 2 Mineral percentages in increasingly saline pans 17 through 1 (refer to figure 5 for brine chemistry). and 1) precipitate. The brines of Page 5 www.saltworkconsultants.com

(27%) and a minimum in October (15%) and with a peak tents in the various lakes range from 165 to 360 g/l, with in the morning when it may reach 50%. The low relative pH ranging between 5.4 and 7.85. Today the salt plain and humidity and the high insolation (direct radiation of 3000 pans of the Qarhan playa are fed mostly by runoff from kWh m−2 yr−1) in the salt flat increase the efficiency of solar the (Kunlun Shan), along with input evaporation, giving rise to the precipitation and stability from a number of saline groundwater springs concentrated of very deliquescent minerals, such as carnallite and bis- along a fault trend defining an area of salt karst along the chofite. The average annual evaporation value measured in northern edge of the Dabuxum sump, especially north of the period 1998–2011, using the salt flat interstitial brine, Xiezuo Lake (Figure 8a). is approximately 2250 mm with a peak in December–Jan- The present climate across the Qaidam Basin is cool, arid uary and a minimum in June–July. This cool high altitude to hyperarid (BWk), with an average annual rainfall of 26 hyperarid climatic setting where widespread sylvite and mm, mean annual evaporation is 3000–3200 mm, and a carnallite accumulates on the pan floor is different from mean annual temperature 2-4° C in the central basin (An that envisaged in ancient marine-fed potash basins (as dis- et al., 2012). The various salt lakes and playas spread across cuseed in the upcoming third article in this series). the basin and contain alternating climate-dependent evap- MOP from brine Dabuxum/Qarhan re- oritic sedimentary sequences. Across the basin the playa gion, Qaidam Basin, Fault trend de ned China by salt karst springs A. The Qarhan saltflat/playa is now Senie Lake the largest hypersaline sump Beihubuxum Lake within the disaggregated lacus- trine system that makes up the Fan Dabiele Lake Dabuxum Lake hydrology of Qaidam Basin, Potash pans China (Figure 7a). The Qaidam basin sump has an area of some Figure 2. 6,000 km2, is mostly underlain Tuanji Lake by bedded Late Quaternary ha- lite. Regionally, the depression is endorheic, fed by the Golmud, Qarhan and Urtom (Wutu- meiren) rivers in the south and Kunlun Mountains the Sugan River in the north, and today is mostly covered by a layered halite pan crust. Be- 94°00’ 94°30’ 95°00’ 95°30’ 96°00’ low, some 0 to 1.3m beneath the B. Bieletaan 20 km playa surface, is the watertable BLT Dabuxun 37°20’ atop a permanent hypersaline 37°20’ DBX 0 Qarhan groundwater brine lens (Figure Huobuxum W-river 20 HBX 7b). 40 60 QJ-river 40 Senie DX 20 45 The southern Qaidam sump en- 70 DBX 37°00’ 37°00’ 20 trains nine perennial salt lakes: XZ BHB DBL Seni, Dabiele, Xiaobiele, Daxi, QD-river

Dabuxum (Dabsan Hu), Tuan- XG-river TJ NHB jie, Xiezuo and Fubuxum north TL-river 0 DG-river 36°40’ 36°40’ NM-river and south lakeshore (Figure 7). Playa Salt Lake 2020 Isopach of evaporite Dabuxum Lake, which occupies strata in metres the central part of the Qarhan 94°00’ 94°30’ 95°00’ 95°30’ 96°00’ sump region, is the largest of the DongGolmud (DG) River QuanJi (QJ) River Beihuobuxum (BHB) Lake Nanhuobuxum (NHB) Lake 2 NuoMuhong (NM) River Wutumieren (W) River Dabiele (DBL) Lake Tuanji (TJ) Lake perennial lakes (184 km ; Fig- QaiDam (QD) River XiGolmud (XG) River Dabuxum (DBX) Lake Xiezhuo (XZ) Lake ures 7b, 8a). Lake water depths Xidabuxum (DX) Lake vary seasonally from 20cm to 1m Figure 7. Lakes and saltflats in the southern portion of the Qaidam Basin, China. A) Locality map of and never deeper than a metre, region centred on the Golmud Fan (Landsat image courtesy of NASA < https://zulu.ssc.nasa.gov/ even when flooded. Salt con- mrsid>). B) Map showing distribution of evaporite beds and salt lakes on the downflow side of the Golmud bajada. Page 6 www.saltworkconsultants.com

Layered carnallite Donglin Lake Stratoid carnallite Fault Disseminated carnallite Perennial saline lake Playa mud at

Dabuxum Xiezuo Lake Senie Daxi X Lake Fubuxum Lake Xiaobiele Lake Dadong Lakes Lake W. Golmud ancient Urtom Dabiele River Lake Qarhan River River Lake Tuanje Lake X’ E. Golmud 0 30km Sugang A. River River Clay-silt Increasing potash Tuanje parting layer X Lake X’ Halite Carnallitite Silty halite Gypsiferous 0 2 4 km silt 0 2 B. 4m Dadong ancient lake Figure 8. Potash in the southern Qaidam Basin (after Duan and Hu, 2001). A) Geological plan, map position indicated by white rectangle in Figure 7a. B) Schematic cross section X-X' across Tuanje Lake, showing transition from halite to potash in a northerly direction )in part after Duan and Hu, 2001). sumps are surrounded by aeolian deposits and wind-erod- ever the salt crust lies above the watertable. Interbedded ed landforms (yardangs). In terms of potash occurrence, salts and siliciclastic sediments underlying the crust reach the most significant region in the Qaidam Basin is the Qa- thicknesses of upwards of 70m (Kezao and Bowler, 1985). rhan sump or playa (aka Chaerhan Salt Lake), which occu- Bedded potash, as carnallite, precipitates naturally in tran- pies a landscape low in front of the outlets of the Golmud sient volumetrically-minor lake strandzone (stratoid) beds and Qarhan rivers (Figure 7a, b). Overall the Qaidam Ba- about the northeastern margin of Lake Dabuxum (Figure sin displays a typical exposed lacustrine geomorphology 8a) and as cements in Late Pleistocene bedded deposits ex- and desert landscape, related to increasing aridification in posed in and below nearby Lake Tuanje in what is known a cool desert setting. In contrast, the surrounding elevated as the sediments of the Dadong ancient lake (Figure 8b). highlands are mostly typified by a high-alpine tundra (ET) Ongoing freshened sheetflow from the up-dip bajada fans Köppen climate. means the proportion of carnallite versus halite in the Bedded and displacive salts began to accumulate in the Qa- evaporite unit increases with distance from the Golmud rhan depression some 50,000 years ago (Figure 9). Today, Fan across both the layered (bedded) and stratoid (cement) outcropping areas of surface salt crust consists of a chaotic modes of occurrence. mixture of fine-grained halite crystals and mud, with a rug- At times in the past, when the watertable was lower, oc- ged, pitted upper surface (Schubel and Lowenstein, 1997; casional meteoric inflow was also the driver for the brine Duan and Hu, 2001). Vadose diagenetic features, such as cycling that created the karst cavities hosting the halite dissolution pits, cavities and pendant cements, form wher- Page 7 www.saltworkconsultants.com

CORE 89-04 Primary halite 0 chevron and cumulative halite Mud; massive to vaguely layered carnallite cement Laminated mud halite cement Halite cements in halite crusts 10 displacive halite

Carnallite cements displacive carnallite in halite crusts DEPTH (M) Displacive halite crystals in mud Displacive carnallite 20 Northern margin crystals in mud Dabuxun Lake Displacive gypsum salt at Carnallite-saturated brines 1.30 crystals in mud 1.20 10 20 30 40

sediment age 30 depth U-series date primary (m) (Ka. BP) halite 8.8 10.4±2.2 17.2 22.4±1.7 mud 22.8 25.0±1.8 40 0 26.4 27.6±4.5 32.6 37.6±2.5 0 150m 37.2 48.1±6.5 5m 42.8 54.5±4.5 Cross section of Dabuxum northern strandline Brine Brine density temp (°C) Figure 9. Carnallite in halite, illustrated in a cross section and in recovered core textures collected in evaporitic sediment beneath the northen margin of Lake Dabuxum, China (after Casas and Lowenstein, 1992). and carnallite cements that formed as prograde cements low halite beds to accumulate, occurred a number of times during cooling of the sinking brine (Figure 9). Solid bed- in the Late Quaternary: 1) in a short-lived event ≈ 50,000 ded potash salts are not present in sufficient amounts to be ka, 2) from about 17 - 8,000 ka, and 3) from about 2,000 quarried and most of the exploited potash resource resides ka till now (Figure 9). in interstitial brines that are pumped and processed using The greatest volume of water entering Dabuxum Lake solar ponds. comes from the Golmud River (Figure 7b). Cold springs, Modern halite crusts in Qarhan playa contain the most emerging from a linear karst zone some 10 km to the north concentrated brine inclusions of the sampled Quaternary of the Dabuxum strandline and extending hundreds of km halites, suggesting that today may be the most desiccated across the basin, also supply solutes to the lake. period in the Qarhan-Tuanje sump recorded over the last The spring water that discharge along this fault-defined 50,000 years (values in the inset in figure 9 were measured karst zone is chemically similar to the hydrothermal Ca– on clear halite-spar void-fill crystals between chevrons). Cl sourced waters and are interpreted as subsurface brines Inclusion measurements from these very early diagenetic that have risen to the surface along deep faults to the north halite show they formed syndepositionally from shallow of the Dabuxum sump (Figure 9, 10; Spencer et al., 1990; groundwater brines and confirm the climatic record de- Ma et al., 2001; Lowenstein and Risacher, 2009). Depths rived from adjacent primary (chevron) halite. The occur- from where the Ca–Cl spring waters rise is not known. rence of carnallite-saturated brines in fluid inclusions in Subsurface lithologies of the Qaidam Basin in this region the diagenetic halite in the top 13 m of Qarhan playa sed- contains Jurassic and younger sediments and sedimentary iments also imply a prograde diagenetic, not depositional, rock columns, up to 15 km thick, which overlie Proterozoic origin of carnallite, which locally accumulated in the same metamorphic rocks (Wang and Coward, 1990). voids as the more widespread microkarst halite-spar ce- ments. It is also possible that Ca–Cl waters rise to the surface along a focusing permeability boundary between alluvial Today, transient surficial primary carnallite rafts can accu- fan-dune sediments to the north and less permeable salt- mulate along the northern strandline of Lake Dabuxum mud sediments of the Qarhan sump to the south. Spring (Figure 9; Casas, 1992; Casas et al., 1992). Compositions inflows, whatever the flow path, have created an at-sur- of fluid inclusions in the older primary (chevron) halite face karst zone, focused along the main fault cutting the beds hosting carnallite cements in the various Qarhan salt sump and is defined by a series of depressions, where rising crusts represent preserved lake brines and indicate relative- spring waters have dissolved soluble Neogene evaporites. ly wetter conditions throughout most of the Late Pleisto- cene (Yang et al., 1995). Oxygen isotope signatures of the Figures 10a and 11a plot the range of chemistries shown inclusions record episodic freshening and concentration by inflows and evolving brines in the Qarhan sump. Both during the formation of the various salt units interlayered plots show that Cl is a relatively conservative ionic compo- with lacustrine muds. Desiccation events, sufficient to al- nent across all waters in the sump (Cl dominates the ionic

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A. ++ 12 Mg Saline karst and lake brines Na+ - HCO3 10 K+ -- SO4 Cl- 8 Ca++

Mg conservative 6 Molality

4

2 CaCl2 brine trend inflow Na decrease 0 1.05 1.10 1.15 1.20 1.25 1.30 1.35 1.40 Density (gm/cc)

Ca Ca Ca B. C. D. K DG, XZ Karst Karst QAIDAM BASIN Springs QAIDAM BASIN Spring N. H QAIDAM BASIN EVAPORATION NFLOW S-R Mixing I H S-R Mixing SURFACE 15R:1S WATERS WATERS Ca-Cl DS WATERS Ca-Cl Gypsum Gypsum Gypsum Ca-Cl Calcite 40R:1S Calcite Calcite Anhydrite Anhydrite Anhydrite DS WR Qaidam River 56R:1S Cl-SO4 Cl-SO Golmud River 4 DS Cl-SO SW Urtom River 4 Golmud W. DS River Na-HCO -SO Na-HCO -SO 100R:1S DS 3 4 3 4 Na-HCO -SO W. DS 100R:1S 3 4 DBL DS S SO HCO -alkalinity SO HCO -alkalinity T XB DS HCO -alkalinity 4 3 4 3 SO4 3 Figure 10. Qaidam Basin waters. A) Qarhan Lake basin waters showing general ionic trends (molalities) plotted against increasing density. Plot is constructed from water chemistry data as listed in Table 2 in Spencer et al., 1990. B) Qaidam Basin inflow water compositions. WR is world average river water, SW is modern seawater. C) Evaporation paths for mixtures of river water (Golmud River) and karst spring inflow. S–R is a mixing line between spring water (karst spring) and river water (Golmud River). D) Qaidam Basin surface brine lake compositions (DG, Donglin; XZ, Xiezhuo; NH, North Huobusun; H, Huobusun; K, karst brine pond; WDS, West Dabuxun; DS, Dabuxun; S, Senie, DBL, Dabiele; XB, Xiaobiele;

T, Tuanjie) (B-C-D Ternary Ca–SO4–HCO3 phase diagrams after Lowenstein and Risacher, 2009).

water proportions at all stages from inflow to bittern). The ters, after precipitation of calcite and gypsum, evolve into ++ Mg trend tends to flatten at higher densities and salini- Ca–Cl-rich, HCO3–SO4-poor brines (brines numbered 5, ties, indicating carnallite is a natural precipitate at densities 7-12 in figure 11a). in excess of 1.26 gm/cc and TDS in excess of 300,000ppm. + Dabuxum is the largest lake in the Qarhan region, with Na levels in the various brines tends also to decrease be- brines that are Na–Mg–K–Cl dominant, with minor Ca yond such values due to halite precipitation. and SO4 (Figure 10d, 11a). These brines are interpreted Several lakes located near the northern karst zone (Don- by Lowenstein and Risacher (2009) to have formed from a glin, North Huobusun, Xiezhuo, and Huobusun) receive mix of ≈40 parts river water to 1 part spring inflow, so that

sufficient Ca–Cl inflow, more than 1 part spring inflow to the equivalents of Ca ≈ equivalents HCO3 + SO4 (Fig- 40 parts river inflow, to form mixtures with chemistries of ure 10b). Brines with this ratio of river to spring inflow

Ca equivalents > equivalents HCO3 + SO4 to create a sim- lose most of their Ca, SO4, and HCO3 after precipitation ple potash evaporation series (this is indicated by the Ca- of CaCO3 and CaSO4, and so form Na–K–Mg–Cl brines Cl trend line in Figure 10a). With evaporation such wa- capable of precipitating carnallite and sylvite (Figure 11a).

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106 Figure 11b clearly illustrates sul- 8. 9. 10., 11., 12. 3. 5. 6.7. Cl 4. phate to chloride variation in pore 105 waters in the region to the imme- 1. Golmud River Na 1. 2. Daqaidam hot spring Mg diate north and east of Dabuxum 104 3. Karst pond (fault fed)* Ca Lake. Brine wells in the low-sul- 4. Lake Xiaoqaidam phate area are drawn upon to sup- 5. Inlet brine (to pans)* K 103 6. Lake Chaka ply feeder brines to the carnallite 1., 2.,1. SO 7. Halite pan* 4 precipitating ponds. The hydro- 8. Carnallite pan* 2 chemistry of this region is a clear 10 9. Lake Dabuxun* ion concentration (ppm) 10. Bischo te pan* indication of the regional variation 11. Carnallite pan* in the sump hydrochemistry (Ma et 101 12. Carnallite pan* al., 2001), but also underlines why it is so important to understand 1 porechemistry, and variations in 5 5 5 5 A.0 1 10 2 10 3 10 4 10 aquifer porosity and permeability TDS (ppm) when designing a potash plant in a Concentrations in intercrystalline brines Quaternary saline setting. in the Qarhan Lake region Compared to the MOP plant in Atacama there as yet no lithium carbonate extraction stream to 20 help ameliorate costs associated Dabuxum Lake with carnallite processing. Lithium levels in the Qaidam brines while elevated are much lower than in the Atacama brine feeds. Region- ally, away from the Tuanje-Dadong 2 15 area, most salt-lake and pore brines Chloride dominant 4 in the Qaidam flats are of the mag- Sulphate dominant nesium sulphate subtype and the 6 10 ratio of Mg/Li can be as high as 10 Ca ppm 10 500. With such brine composi- 10 5 tions the chemical precipitation SO ppm 30 4 approach that is successfully ap- B. plied to Lithium extraction using Figure 11. Hydrochemical varitions in the Qaidam sump, China. A) Regional variation in salinity and low calcium and magnesium brines ionic proportions, showing an obvious dichotomy between sulphate-enriched and suphate-depleted (such as those from Zabuye and waters. Sulphate-depleted waters indicated by *. (replotted from Vengosh et al., 1995). B) Sulphate dichomoty in the pore waters in the vicinity of Dabuxum Lake . Note the potash pans draw on sulphate Jezecaka Lake on the Tibetan Pla- depleted pore waters (after Duan and Hu., 2001). teau and in the Andean Altiplano) would consume a large quantity

This chemistry is similar to that of ancient MgSO4-depla- of chemicals and generate a huge eted marine bitterns (Figure 1) amount of solid waste. Accordingly, brine operations are focused on MOP production from a carnallitite slurry us- The chemical composition of surface brines in the vari- ing extraction techniques similar to those in the Southern ous lakes on the Qarhan Salt plain vary and appear to be Dead Sea, but owing to its cooler climate the pond chem- controlled by the particular blend of river and spring in- istry is subject to lower evaporation rates, higher moisture flows into the local lake/playa sump. In turn, this mix is levels in the product and a longer curing time. controlled geographically by proximity to river mouths and the northern karst zone Formation of marine-like ionic Potash in the Qarhan region is produced by the proportions in some lakes, such as Tuanje, Dabuxum and Salt Lake Potash Company, which owns the 120-square-ki- ancient Dadong Lake, engender bitterns suitable for the lometer salt lake area near Golmud (Figure 7). The com- primary and secondary precipitation of sylvite/carnallite pany was established and listed on the Shenzhen Stock (Figures 10b-d; 11a). The variation in the relative propor- Exchange in 1997. Currently, it specializes in the manu- tion of sulphate to chloride in the feeder brines is a funda- facture of MOP from the lake sediments and its brines. mental control on the suitability of the brine as a potash The MOP factory processes a carnallite slurry pumped producer. from pans with the appropriate salinities using a process- Page 10 www.saltworkconsultants.com

Figure 12. Tuanje (MOP) pans, China, with a carnallite dredge in the left midground and the processing plant in the right background of image. ing stream very similar to the dual process stream utilized the perennial lake is ongoing dissolution of the halokinetic in the pans of the Southern Basin in the Dead Sea and salts of the Miocene Sedom Fm (aka Usdum Fm) a marine discussed in the next section. evaporite unit that underlies the Dead Sea and approaches the surface in diapiric structures beneath the Lisan Straits The final potash product in the Qaidam sump runs 60-62% and at Mt. Sedom (Garfunkel and Ben-Avraham, 1996). K2O with >2% moisture and is distributed under the brand name of “Yanqiao.” With annual production ≈3.5 million A series of linked fractionation ponds have been built in tonnes and a projected reserve ≈ 540 million tonnes, the the Southern Basin of the Dead Sea to further concentrate company currently generates 97% of Chinese domestic pumped Dead Sea brine to the carnallite stage (Figure 13). MOP production. However, China’s annual agricultural On the Israeli side this is done by the Dead Sea Works need for potash far outpaces this level of production. The Ltd. (owned by ICL Fertilisers), near Mt. Sedom, and by company is jointly owned by Qinghai Salt Lake Industry the Arab Potash Company (APC) at Ghor al Safi on the Group and Sinochem Corporation and is the only domes- Jordanian side. ICL is 52.3% owned by Israel Corporation tic producer of a natural MOP product. Ltd.(considered as under Government control), 13.6% shares held by Potash Corporation of Saskatchewan and Dead Sea Potash (MOP operation in the 33.6% shares held by various institutional investors and Southern Basin) general public (33.64%). In contrast ,PotashCorp owns The Dead Sea water surface defines what is the deepest 28% of APC shares, the Government of Jordan 27%, Arab continental position (-417 m asl) on the earth’s current ter- Mining Company 20%, with the remainder held by several restrial surface. In the Northen Basin is our only modern small Middle Eastern governments and a public float that example of bedded evaporitic sediments (halite and gyp- trades on the Amman Stock Exchange. This gives Potash- sum) accumulating on the subaqueous floor of a deep brine Corp control on how APC product is marketed, but it does body, where water depths are hundreds of metres (Warren, not control how DSW product is sold. 2016). This salt-encrusted depression is 80 km long and 20 In both the DSW and APC brine fields, muriate of pot- 2 km wide, has an area of 810 km , is covered by a brine vol- ash is extracted by processing carnallitite slurries, created 3 ume of 147 km and occupies the lowest part of a drainage by sequential evaporation in a series of linked, gravity-fed 2 basin with a catchment area of 40,650 km (Figure 13a). fractionation ponds. The inflow brine currently pumped However, falling water levels in the past few decades mean from the Dead Sea has a density of ≈1.24 gm/cc, while the permanent water mass now only occupies the northern after slurry extraction the residual brine, with a density part of the lake, while saline anthropogenic potash pans of ≈1.34 gm/cc, is pumped back into the northern Dead occupy the southern basin, so that the current perennial Sea basin water mass. The total area of the concentration “Sea” is now only some 50 km long. pans is more than 250 km2, within the total area of 1,000 2 Rainfall in the region is 45 to 90 mm, evaporation around km , which is the southern Dead Sea floor. The first stage 1500 mm, and air temperatures between 11 and 21°C in in the evaporation process is pumping of Dead Sea water winter and 18 to 40°C in summer, with a recorded max- into header ponds and into the gravity-fed series of artifi- imum of 51° C. The subsiding basin is surrounded by cial fractionation pans that now cover the Southern Basin mountain ranges to the east and west, producing an oro- floor. With the ongoing fall of the Dead Sea water lev- graphic rain shadow that further emphasises the aridity of el over the past 60 years, brines from the Northern Basin the adjacent desert sump. The primary source of solutes in must be pumped higher and over further lateral distances. This results in an ongoing need for more powerful brine Page 11 www.saltworkconsultants.com

Jordan Northern A. B. North River 500 C. Basin 600 Lisan Peninsula 700 Dead Sea 0 10 conveying km canal

728 NORTHERN BASIN Halite Southern ponds Basin (DSW)

Rift Brine escapment conveying canal Arnon River 31° 20’ Carnallite ponds DSW solar 5 km evaporation Zone of most pans 400 intense salt reef growth 900 700 31° 10’ SOUTHERN 500 BASIN 300 APC solar Halite Carnallite evaporation Deposition (g/l brine) 100 10 km Mt Sedom pans 35° 30’ 1.22 1.26 1.30 1.34 Density Figure 13. Dead Sea Potash production. A) Evaporation pans at the southern end of the Dead Sea (2000 Landsat image courtesy of NASA). B) The water surface in the Dead Sea is around 417 m below sea level. The Southern Basin (elevation more than -401m msl) is covered only by a thin controlled brine sheet up to 2 metres deep in a series of concentrator pans maintained by pumping of brines from the Northern Basin where waters attain depths of more than 300m, seafloor isobaths are in metres below sea level. C) Design of sequential evaporation pans at the Israeli Sedom plant, southern Basin of the Dead Sea, colour coded to show the relationship between increasing concentration (density) and the transition from halite to carnallite precipitation ponds, and the associated brine densities (after Karcz and Zak, 1987). pumps and an increasing problem with karst dolines re- 2 metres. During the early halite concentration stages, a lated to lowered Dead Sea water levels. Saturation stages series of problematic halite reefs or mushroom polygons of the evolving pan brines are monitored and waters are can build to the brine surface and so compartmentalise moved from pan to pan as they are subject to the ongoing and entrap brines within isolated pockets enclosed by the and intense levels of natural solar evaporation (Figure 13b, reefs. This hinders the orderly downstream progression of c; Karcz, 1987). increasingly saline brines into the carnallite ponds, with the associated loss of potash product. The artificial salt ponds of the Dead Sea are unusual in that they are designed to trap and discard most of the halite When the plant was first designed, the expectation was precipitate rather than harvest it. Most other artificial salt that halite would accumulate on the floor of the early frac- ponds around the world are shallow pans purpose-designed tionation ponds as horizontal beds and crusts, beneath as ephemeral water-holding depressions that periodical- permanent holomictic brine layers. The expected volume ly dry out so that salts can be scrapped and harvested. In of salt was deposited in the pans each year (Talbot et al., contrast, the Dead Sea halite ponds are purpose-designed 1996), but instead of accumulating on a flat floor aggrad- to be permanently subaqueous and relatively deep (≈4m). ing 15-20 cm each year, halite in some areas aggraded into Brine levels in the ponds vary by a few decimetres during a series of polygonally-linked at-surface salt reefs (aka salt the year, and lowstand levels generally increase each winter mushrooms). Then, instead of each brine lake/pan being when waste brine is pumped back into the northern basin. homogenized by wind shear across a single large subaque- ous ponds, the salt reefs separated the larger early ponds As the Dead Sea brine thickens, minor gypsum, then volu- into thousands of smaller polygonally-defined inaccessible minous halite precipitates on the pan floor in the upstream compartments, where the isolated brines developed differ- section of the concentration series, where the halite-precip- ent compositions (Figure 14). Carnallitite slurries crystal- itating-brines have densities > 1.2 gm/cc (Figure 13c). As lized in inter-reef compartments from where it could not be the concentrating brines approach carnallite-precipitating easily harvested, so large volumes of potential potash prod- densities (around 1.3 gm/cc), they are allowed to flow into uct were locked up in the early fractionation ponds(Figure the carnallite precipitating ponds (Figure 13c). Individual 2 14a, b). Attempts to drown the reefs by maintaining fresh- pans have areas around 6-8 km and brine depths up to Page 12 www.saltworkconsultants.com

Isolated water volume pumped into the brine pond pond has been halved. Concen- trated halite-depleted brine is then pumped through a convey- Carnallite ance canal into a series of smaller evaporation ponds where carnal- lite, along with minor halite and gypsum precipitates (Figure 13c). Around 300–400 mm of carnal- lite salt slurry is allowed to ac- cumulate in the carnallite ponds, with 84% pure carnallite and 16% sodium chloride as the average chemical composition (Figure 6a; Abu-Hamatteh and Al-Amr, 2008). The carnallite bed is har- vested (pumped) from beneath B. C. the brine in slurry form and is Isolated delivered through corrosion-re- brine pond sistant steel pipes to the process refineries via a series of powerful pumps. Coalesced halite mushrooms form edge to isolated ponds Mushroom dredge This carnallitite slurry is harvest- ed using purpose-specific dredg-

Figure 14. Effects of salt mushroom (halite ridge) growth in the halite pans of the saltworks in the es floating across the crystalliser southern Dead Sea. A) Carnallite growing in a ridge-isolated section in the main halite pan zone. ponds. These dredges not only B) Coalesced halite reefs (mushrooms) merging to form isolated shallow ponds containing brine that pump the slurry to the process- can then reach carnallite saturation. C) A dredge, sometimes used in combination with explosives, to ing plant but also undertake the break up the halite polygon networks in the halite pans. ened waters in the ponds during 5, 6, 7, 8 9 10, 11 the winters of 1984 and 1985 were 1 10 3 4 only partly successful. The current approach to the salt reef problem in the early fractionation ponds is 1 to periodically breakup and remove 1, 2 Na the halite reefs and mushrooms by -1 10 Cl a combination of dredging and oc- Mg casional blasting (Figure 14c). 10-2 Ca Unlike seawater feeds to conven- K Ion concentration (eq/L) tional marine coastal saltworks SO4 10-3 producing halite with marine in- HCO3 flow salinities ≈35‰, the inflow brine pumped into the header 10-4 ponds from the Dead Sea already 0 100 200 300 400 500 600 has a salinity of more than 300‰ TDS (g/L) (Figure 15). Massive halite pre- 1. Jordan River 1970 6. Dead Sea; upper water 1975 - 1976 cipitation occurs quickly, once the 2. Jordan River 2000 7. Dead Sea; lower water mass 1975 -1976 brine attains a density of 1.235 3. Average subsurface aquifer 8. Dead Sea; homogenous 2006 (≈340‰) and reaches a maxi- 4. Dead Sea; upper water 1956-1970 9. End brine 1985 (post-carnallite) mum at a density of 1.24 (Figure 5. Dead Sea; lower water mass 1956-1970 10. Sink hole in salt 9/2006 (Shalem) 13c). Evaporation is allowed to 11. Sink hole in salt 7/2007 (Shalem) continue in the initial halite con- Figure 15. Hydrochemical evolution of the inflow and surface waters in the Dead Sea and surrounds centrator ponds until the original (replotted from data in Table 1 in Katz and Starinsky, 2009). Note the low-sulphate chemistry of the Dead Sea brine feed. Page 13 www.saltworkconsultants.com

early part of the processing stream. Brines pumped to Southern Basin concentration Northern On the dredge, harvested slurry Dead Sea is crushed, size sorted, with the coarser purer crystals separated for cold . The remain- der is slurried with the residual pan brine and then further filtered Salt pans (1.2-1.3 gm/cc) Pre-carnallite pan Carnallite pans >1.34 gm/cc aboard the floating dredges. At NaCl precipitates >1.3 gm/cc Carnallitite slurry (20-35% solids) this stage in the processing stream the dredges pipe the treated slur- ries from the pans to the refining plant. Hot Leach Plant On arrival at the processing plant, KCl this raw product is then used to Cold Crystallisation Plant manufacture muriate of potash, A. salt, , magne- sium oxide, hydrochloric acid, bath O) salts, chlorine, caustic soda and 700 2 14 magnesium metal (Figure 16a). 10 Residual brine after carnallitite 600 precipitation contain about 11- 6 12 g/l bromide and is used for the Carnallite 2 500 /L 0 20 40 60 80 production of bromine, before the 2 KCl.MgCl2.6H2O waste brine (with a density around (mole/1000 mole H KCl T (°C) O)

1.34 gm/cc) is returned to the 2 6 g MgCl 400 Sylvite KCl northern Dead Sea water mass. 100°C The entire cycle from the slurry 5 300 80 harvesting to MOP production 60 4 0°C 40 takes as little as five hours. 25 200 3 In the initial years of both DSW 0 20 40 80 80 100 120 0 20 40 60 80 and APC operations, MOP was g KCl/L NaCl (mole/1000 mole H T (°C) refined from the carnallite slurry B. C. via hot leaching and flotation. In Figure 16. Dead Sea (MOP) brine chemistry. A) Process stream for MOP manufacture in Dead Sea brine pans (Blue arrows indicate solar evaporation). B) Cold Crystallization based on incongruent the coarser-crystalline carnallitite dissolution and illustrated by carnallite/KCl curve in the presence of 3% NaCl (after Mansour and feed, significant volumes of syl- Takrouri, 2007). C) Hot or thermal crystallization is based on fact that halite solubility does not change vite are now produced more eco- greatly with temperature, while KCl solubility trebles over the same range. Different coloured symbols nomically in a cold crystallization indicate different experimental runs (after Karcz and Zak, 1987). plant (Figure 16b). The cold crys- KCl solubility is suppressed to the point where most of tallization process takes place at ambient temperature and it will precipitate as sylvite. For maximum recovery, the is less energy-intensive than the hot crystallization unit. crystallizing mixture must be saturated with carnallite at The process also consumes less water but requires a higher its triple-saturation point. If the mixture is not saturated, and more consistent grade of carnallite feed (Mansour and for example, it contains higher levels of NaCl, then more Takrouri, 2007; Abu-Hamatteh and Al-Amr, 2008). Both KCl will dissolve during the water flushing of the slurry. hot (thermal) and cold production methods can be utilized Industrially, the cold crystallizers are usually fed with both in either plant, depending on the quality of the slurry feed. coarse and fine carnallite streams, such that 10% carnallite Sylvite is produced via cold crystallization using the ad- remains in the slurry, this can be achieved by adjusting ad- dition of water to incongruently dissolve the magnesium dition of process water (Mansour and Takrouri, 2007). chloride from the crystal structure. If the carnallite slurry Successful cold crystallization depends largely on a high contains only a small amount of halite, the solid residue quality carnallite feed. If a large amount of halite is present that remains after water flushing is mostly sylvite. As is in the feed slurry, the resulting solid residue from cold crys- shown in Figure 16b, if the MgCl2 concentration is at or tallization is sylvinite, not sylvite. This needs to be further near the triple-saturation point (the point at which the refined by hot crystallization, a more expensive extraction is saturated with carnallite, NaCl, and KCl), the method based on the fact that the solubility of sylvite var- Page 14 www.saltworkconsultants.com

ies greatly with increasing tem- perature, while that of salt remains relatively constant (Figure 16c). As potash brine is hot leached from the sylvinite, the remaining halite is filtered off, and the brine is cooled under controlled condi- tions to yield sylvite. Residual brine from the crystalli- zation processes then undergoes electrolysis to yield chlorine, caus- tic soda () and hydrogen. Chlorine is then reacted with brine filtered from the pans to produce bromine. The caustic soda is sold, and the hydrogen is used to make bromine compounds, with the excess being burnt as fuel. Bromine distilled from the brine is sold partly as elemental bromine, and partly in the form of bromine compounds produced in the bro- mine plant at Ramat Hovav (near Beer Sheva). This is the largest bromine plant in the world, and Israel is the main exporter of bro- mine to Europe. About 200,000 tons of bromine are produced each year. Residual magnesium chloride-rich created by cold crystalli- zation are concentrated and sold as flakes for use in the chemical Figure 17. Part of the Dead Sea saltworks processing factory on the Israeli side of the Southern Basin. industry and for de-icing (about 100,000 tons per year) and dirt tinuing with an expansion program aimed at increasing road de-dusting. Part of the MgCl2 solution produced is potash capacity to 2.5 Mt/yr. sold to the nearby Dead Sea Periclase plant (a subsidiary of Israel Chemicals Ltd.). At this plant the brine is de- MOP brines and Quternary climate composed thermally to give an extremely pure magnesi- As mentioned in the introduction, exploited Quaternary um oxide (periclase) and hydrochloric acid. In Israel, Dead potash deposits encompass both MOP and SOP mineral Work’s (DSW) production has risen to more than associations across a range of climatic and elevation set- 2.9 Mt KCl since 2005, continuing a series of increments tings. This article focuses on the three main MOP pro- and reflecting and investment in expanded capacity, the ducing examples, the next deals with SOP Quaternary streamlining of product throughput in the mill facilities, producers (Great Salt Lake, USA and Lop Nur, China). and the amelioration of the effects salt mushrooms, and Interestingly, both sets of Quaternary examples are non- increased salinity of the Dead Sea due to extended drought marine brine-fed depositional hydrologies. All current- conditions. On the other side of the truce line in Jordan, ly-active economic potash plants hosted in Quaternary the Arab Potash Co. Ltd. (APC) output rose to 1.94 Mt systems do not mine a solid product but derive their potash KCl in 2010 THe APC plant now has the capacity to pro- solar evaporation of pumped hypersaline lake brines. For duice 2.35 Mt KCl and like the DSW produces bromine MOP processing to be economic the sulphate levels in the from bittern end birnes. Early in the brine concentaration brines held in bittern-stage concentrator pans must be low stream APC also has to remove salt mushrooms from its and Mg levels are typically high, so favoring the precipita- ponds, a process which when completed can increase car- tion of carnallite over sylvite in all three systems. nallite output by over 50 000 t/yr. Currently, APC is con- Page 15 www.saltworkconsultants.com

In Salar de Atacama the low ET EF sulphate levels in the bittern Am A. Af *Big Quill Lake Inder Lake As *Wendover stage is accomplished by arti- Pilot Aw *Lop Nur Valley *Great Salt Lake Tuz Golu Urmia Lake ficially mixing a CaCl brine BWk Sevier Lake *Dabuxum 2 BWh Chott el Djerid Khour playa Cerro Prieto BSk *Dead Sea from further up the evaporation BSh Edri Marada Cfa Was an Namus Umm as Samim stream with a less saline more Cfb Cfc Dallol sulphate-enriched brine. The Csa Csb mixing proportions of the two Csc Cwa brine streams aims to maximise Cwb Bayovar Cwc the level of extraction/removal Dfa Dfb Lake Disappointment *Salar de Atacama of CaSO4 in the halite pans pri- Dfc Lake Mackay Dfd Salar Gorbea Salar de Diabillos Lake Macleod or to the precipitation of sylvite Dsa Salar de Pedernales Laguna Verde Karinga Ck. Lake Barlee Dsb Salar de Maricunga Lake Chandler and carnallite. In the case of the Dsc (alunite) Dwb pans in the Qarhan sump there Dwd is a similar but largely natu- 5000 ral mixing of river waters with ET fault-fed salt-karst spring wa- Laguna Verde B. Salar de Diabillos ters in a ratio of 40:1 that creates 4000 Salar de Salar Corbea a hybrid pore brine with a low Maricunga Salar de Pedernales sulphate chemistry suitable for 3000 the precipitation of both natural *Dabuxum(BWk) and pan carnallite. In the case *Salar de Atacama BWk 2000 *Wendover BSk of the Dead Sea brine feed, the Sevier BSk *Great Salt Lake inflowing Dead Sea waters are BWh Urmia BSk Elevation (msl) Elevation BSk/Csa Karinga Ck. naturally low in sulphate and 1000 Khour playa Tuz Golu Csa Lake Barlee Lake Mackay Waw an Namus high in magnesium. The large Edri *Lop Nur Lake Lake Disappointment Umm as Samim BWk *Big Quill size of this natural brine feed 0 Chandler Dfb BSk Lake Macleod Bayovar Dallol Marada Chott Djerid Inder systems and its homogeneous Bwh BSk nature allows for a moderate Cerro Prieta *Dead Sea (BSh) 1000 cost of MOP manufacture esti- 40 30 20 10 0 10 20 30 40 50 60 mated in Warren 2016, chapter Latitude (degrees) 11 to be US$ 170/tonne. The Figure 18. Quaternary potash occurrences with commercial potash plants denoted by an asterisk. Qarhan production cost is less A) Distribution of selected Quaternary potash occurrences on a Koeppen climate (climate base from Kottek et al., 2006). Main Climates: A; tropical, B; arid, C; warm temperate, D; snow, E; ≈ US$ 110/tonne but the total polar. Precipitation: W; desert, S; steppe, f: fully humid, s: summer dry, w; winter dry, m; mon- reserve is less than in the brine soonal. Temperature: h; hot arid, k; cold arid, a; hot summer, b; warm summer, c; cool summer, d; system of the Dead Sea. In Sal- extremely continental, F: polar frost, T; polar tundra. Molleweide equal-area projection. B) Distribu- tion of selected Quaternary potash occurrences plotted with respect to altitude, latitude and koppen ar de Atacama region the MOP climate (data for this figure extracted with permission from SaltWork GIS database version 1.8 and cost is likely around US$ 250- compiled in MapInfo®). 270/tonne, but this is offset by the production of a bischofite between the current non-potash climate (BWh - Koep- stage brine suitable for lithium carbonate extraction. pen climate) over the Dallol saltflat in Ethiopia, with its nonmarine brine feed and the former now-buried marine Outside of these three main Quaternary-feed MOP pro- fed potash (SOP)/halite evaporite system. The latter is the ducers there are a number of potash mineral occurrences target of current exploration efforts in the basin, focused in intermontane depressions in the high Andes in what is on sediments now buried 60-120m below the Dallol salt- a high altitude polar tundra setting (Koeppen ET), none flat surface Nowhere in the Quaternary are such dry arid of which are commercial (Figure 17a). Similarly, there a desert climates (BWh) associated with commercial accu- number of non-commercial potash (SOP) mineral and mulations of potash minerals. brine occurrences in various hot arid desert regions in Australia, northern Africa and the Middle East (Koeppen Climatically most commercial potash brine systems in BWh) that we shall look at in the next article. In the Da- Quaternary-age sediments are located in cooler endor- nakhil depression there is the possibility of a future com- heic intermontane depressions (BWk, BSk) or in the case bined MOP/SOP plant (see Salty Matters April 19, 2015; of the Dead Sea an intermontane position in the sump April 29, 2015; May 1, 2015; May12, 2015 and Bastow et of the Dead Sea, the deepest position of any continental al., 2018). In the Danakhil it is important to distinguish landscape on the earth’s surface (-417 msl). The associa-

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tion with somewhat cooler and or less arid steppe climates Garfunkel, Z., and Z. Ben-Avraham, 1996, The structure implies a need for greater volumes of brine to reside in a of the Dead Sea: Tectonophysics, v. 155-176. landscape in order to facilitate the precipitation of signifi- Hardie, L. A., 1984, Evaporites: Marine or non-marine?: cant volumes of potash bitterns (Figure 17a,b). American Journal of Science, v. 284, p. 193-240. In summary, all three currently economic Quaternary Hardie, L. A., 1990, The roles of rifting and hydrothermal MOP operations are producing by pumping nonmarine CaCl2 brines in the origin of potash evaporites: an hy- pore or saline lake brines into a series of concentrator pans. pothesis: American Journal of Science, v. 290, p. 43-106. The final bittern chemistry in all three is a low-sulphate liquour, but with inherently high levels of magnesium that Holt, N. M., J. García-Veigas, T. K. Lowenstein, P. S. Giles, favors the solar pan production of carnallite over sylvite and S. Williams-Stroud, 2014, The major-ion composition that is then processed to produce the final KCl product. of Carboniferous seawater: Geochimica et Cosmochimica The brine chemistry in all three examples imitates the Acta, v. 134, p. 317-334. ionic proportions obtained when evaporating a ancient Holt, R. M., and D. W. Powers, 2011, Synsedimentary sulphate-depleted seawater (Figure 1). The next article dissolution pipes and the isolation of ancient bacteria and will discuss the complexities (the double salt problem at cellulose: Geological Society America Bulletin, v. 123, p. the potash bittern stage when concentrating a more sul- 1513-1523. phate-enriched mother brine. Katz, A., and A. Starinsky, 2009, Geochemical History of References the Dead Sea: Aquatic Geochemistry, v. 15, p. 159-194. Abu-Hamatteh, Z. S. H., and A. M. Al-Amr, 2008, Car- Kezao, C., and J. M. Bowler, 1986, Late Pleistocene evolu- nallite froth flotation optimization and cell efficiency in tion of salt lakes in the Qaidam Basin, Qinghai Province, the Arab Potash Company, Dead Sea, Jordan: Mineral China: Palaeogeography, Palaeoclimatology, Palaeoecolo- Processing and Extractive Metallurgy Review: An Inter- gy, v. 54, p. 87-104. national Journal, v. 29, p. 232 - 257. Lowenstein, T., B. Kendall, and A. D. Anbar, 2014, Chap- Alonso, H., and F. Risacher, 1996, Geochemistry of the ter 8.21. The Geologic History of Seawater, Treatise on Salar de Atacama. 1. Origin of components and salt bal- Geochemistry (2nd Edition), Elsevier, p. 569-621. ance [Spanish]: Revista Geologica de Chile, v. 23, p. 113- 122. Lowenstein, T., and F. Risacher, 2009, Closed Basin Brine Evolution and the Influence of Ca–Cl Inflow Waters: An, J. W., D. J. Kang, K. T. Tran, M. J. Kim, T. Lim, and T. Death Valley and Bristol Dry Lake California, Qaidam Tran, 2012, Recovery of lithium from Uyuni salar brine: Basin, China, and Salar de Atacama, Chile: Aquatic Geo- Hydrometallurgy, v. 117, p. 64-70. chemistry, v. 15, p. 71-94. Braitsch, O., 1971, Salt Deposits: Their Origin and Com- Lowenstein, T. K., 1988, Origin of depositional cycles in a positions: New York, Springer-Verlag, 297 p. Permian ''saline giant''; the Salado (McNutt Zone) evap- Carmona, V., J. J. Pueyo, C. Taberner, G. Chong, and M. orites of New Mexico and Texas: Geological Society of Thirlwall, 2000, Solute inputs in the Salar de Atacama (N. America Bulletin, v. 100, p. 592-608. Chile): Journal of Geochemical Exploration, v. 69, p. 449- Lowenstein, T. K., L. A. Hardie, M. N. Timofeeff, and R. 452. V. Demicco, 2003, Secular variation in seawater chemistry Casas, E., 1992, Modern carnallite mineralisation and Late and the origin of basinal brines: Geology, Pleistocene to Holocene brine evolution in the nonmarine v. 31, p. 857-860. Qaidam Basin, China: Doctoral thesis, State University of Lowenstein, T. K., and R. J. Spencer, 1990, Syndepositional New York at Binghampton. origin of potash evaporites; petrographic and fluid inclu- Casas, E., T. K. Lowenstein, R. J. Spencer, and P. Zhang, sion evidence: American Journal of Science, v. 290, p. 43- 1992, Carnallite mineralization in the nonmarine, Qaidam 106. Basin, China; evidence for the early diagenetic origin of Lowenstein, T. K., M. N. Timofeeff, S. T. Brennan, H. L. potash evaporites: Journal of Sedimentary Petrology, v. 62, A., and R. V. Demicco, 2001, Oscillations in Phanerozoic p. 881-898. seawater chemistry: Evidence from fluid inclusions: Sci- Duan, Z. H., and W. X. Hu, 2001, The accumulation of ence, v. 294, p. 1086-1088. potash in a continental basin: the example of the Qarhan Mansour, A. R., and K. J. Takrouri, 2007, A new technolo- Saline Lake, Qaidam Basin, West China: European Jour- gy for the crystallization of Dead Sea chloride: nal of Mineralogy, v. 13, p. 1223-1233. Chemical Engineering Communications, v. 194, p. 803 -

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810. Pueyo, J. J., G. Chong, and C. Ayora, 2017, Lithium salt- works of the Salar de Atacama: A model for MgSO4-free ancient potash deposits: Chemical Geology. Risacher, F., B. Alonso, and C. Salazar, 2003, The origin of brines and salts in Chilean salars: a hydrochemical review: Earth-Science Reviews, v. 63, p. 249-293. Risacher, F., and H. Alonso, 1996, Geochemistry of Salar de Atacama. 2. Water Evolution [Spanish]: Revista Geo- logica de Chile, v. 23, p. 123-134. Schubel, K. A., and T. K. Lowenstein, 1997, Criteria for the recognition of shallow-perennial-saline-lake halites based on Recent sediments from the Qaidam Basin, western China: Journal of Sedimentary Research Section A-Sedi- mentary Petrology & Processes, v. 67, p. 74-87. Spencer, R. J., T. K. Lowenstein, E. Casas, and P. Zhang, 1990, Origin of potash salts and brines in the Qaidam Ba- sin, China, Special Publication - Geochemical Society, v. 2, p. 395-408. Vreeland, R. H., W. D. Rosenzweig, and D. W. Powers, 2000, Isolation of a 250 million-year-old halotolerant bac- terium from a primary salt crystal: Nature, v. 407, p. 897- 900. Wang, Q., and M. P. Coward, 1990, The Chaidam Basin (NW China): formation and hydrocarbon potential: Jour- nal of Petroleum Geology, v. 13, p. 93-112. Wardlaw, N. C., 1968, Carnallite-sylvite relationships in the middle Devonian Prairie evaporite formation, Sas- katchewan: Geological Society America Bulletin, v. 79, p. 1273-1294. Warren, J. K., 2016, Evaporites: A compendium (ISBN 978-3-319-13511-3): Berlin, Springer, 1854 p. Yang, W. B., R. J. Spencer, H. R. Krouse, T. K. Lowenstein, and E. Cases, 1995, Stable isotopes of lake and fluid inclu- sion brines, Dabusun Lake, Qaidam Basin, Western China - Hydrology and paleoclimatology in arid environments: Palaeogeography Palaeoclimatology Palaeoecology., v. 117, p. 279-290.

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